diff --git a/addon-api/common/Self.js b/addon-api/common/Self.js
index af1f08c66a..d214558726 100644
--- a/addon-api/common/Self.js
+++ b/addon-api/common/Self.js
@@ -1,4 +1,5 @@
 import Listenable from "./Listenable.js";
+import { isFirefox } from "../../libraries/common/cs/detect-browser.js";
 
 /**
  * Represents information about the addon.
@@ -13,8 +14,7 @@ export default class Self extends Listenable {
     this._addonId = info.id; // In order to receive fireEvent messages from background
     this.id = info.id;
     this._addonObj = addonObj;
-    // catches both Chrome and Chromium
-    this.browser = /Chrom/.test(navigator.userAgent) ? "chrome" : "firefox";
+    this.browser = isFirefox() ? "firefox" : "chrome";
     this.disabled = false;
     this.addEventListener("disabled", () => (this.disabled = true));
     this.addEventListener("reenabled", () => (this.disabled = false));
diff --git a/addons-l10n/en/discuss-button.json b/addons-l10n/en/discuss-button.json
new file mode 100644
index 0000000000..08072180bb
--- /dev/null
+++ b/addons-l10n/en/discuss-button.json
@@ -0,0 +1,3 @@
+{
+  "discuss-button/membership": "Membership"
+}
diff --git a/addons/cat-blocks/userscript.js b/addons/cat-blocks/userscript.js
index d492acd69e..04d664722e 100644
--- a/addons/cat-blocks/userscript.js
+++ b/addons/cat-blocks/userscript.js
@@ -358,26 +358,20 @@ export default async function ({ addon, console }) {
       }
     };
   } else {
-    const oldLayout = Blockly.VerticalFlyout.prototype.layout_;
-    Blockly.VerticalFlyout.prototype.layout_ = function (contents, gaps) {
-      const oldStartHeight = Blockly.BlockSvg.START_HAT_HEIGHT;
-      if (!addon.self.disabled) Blockly.BlockSvg.START_HAT_HEIGHT = 31;
-      oldLayout.call(this, contents, gaps);
-      Blockly.BlockSvg.START_HAT_HEIGHT = oldStartHeight;
+    const patchProperty = (object, name, newValue) => {
+      const oldProperty = Object.getOwnPropertyDescriptor(object, name);
+      Object.defineProperty(object, name, {
+        ...oldProperty,
+        get() {
+          if (addon.self.disabled) return oldProperty.get();
+          return newValue;
+        },
+      });
     };
 
-    const oldRenderDrawTop = Blockly.BlockSvg.prototype.renderDrawTop_;
-    Blockly.BlockSvg.prototype.renderDrawTop_ = function (steps, rightEdge) {
-      const oldStartHatPath = Blockly.BlockSvg.START_HAT_PATH;
-      const oldTopCorner = Blockly.BlockSvg.TOP_LEFT_CORNER_DEFINE_HAT;
-      if (!addon.self.disabled) {
-        Blockly.BlockSvg.START_HAT_PATH = CAT_PATH;
-        Blockly.BlockSvg.TOP_LEFT_CORNER_DEFINE_HAT = TOP_LEFT_CORNER_DEFINE_CAT;
-      }
-      oldRenderDrawTop.call(this, steps, rightEdge);
-      Blockly.BlockSvg.START_HAT_PATH = oldStartHatPath;
-      Blockly.BlockSvg.TOP_LEFT_CORNER_DEFINE_HAT = oldTopCorner;
-    };
+    patchProperty(Blockly.BlockSvg, "START_HAT_PATH", CAT_PATH);
+    patchProperty(Blockly.BlockSvg, "TOP_LEFT_CORNER_DEFINE_HAT", TOP_LEFT_CORNER_DEFINE_CAT);
+    patchProperty(Blockly.BlockSvg, "START_HAT_HEIGHT", 31);
 
     const originalRenderDraw = Blockly.BlockSvg.prototype.renderDraw_;
     Blockly.BlockSvg.prototype.renderDraw_ = function (...args) {
diff --git a/addons/custom-zoom/userscript.js b/addons/custom-zoom/userscript.js
index dca84ec5f1..beb8fdb211 100644
--- a/addons/custom-zoom/userscript.js
+++ b/addons/custom-zoom/userscript.js
@@ -65,7 +65,8 @@ export default async function ({ addon, console }) {
       reduxEvents: [
         "scratch-gui/mode/SET_PLAYER",
         "scratch-gui/locales/SELECT_LOCALE",
-        "scratch-gui/theme/SET_THEME",
+        "scratch-gui/settings/SET_COLOR_MODE",
+        "scratch-gui/settings/SET_THEME",
         "fontsLoaded/SET_FONTS_LOADED",
       ],
       reduxCondition: (state) => !state.scratchGui.mode.isPlayerOnly,
diff --git a/addons/dark-www/banners/darker.css b/addons/dark-www/banners/darker.css
index 4a948dae23..6944e40e6d 100644
--- a/addons/dark-www/banners/darker.css
+++ b/addons/dark-www/banners/darker.css
@@ -37,6 +37,7 @@
 .parents .title-banner.masthead .ted-talk {
   border-color: black;
 }
+.membership-page .get-involved-section,
 .educators .title-banner.masthead,
 .educators #teacher-accounts,
 .expect .keynote,
diff --git a/addons/dark-www/banners/desaturated.css b/addons/dark-www/banners/desaturated.css
index 26114ce87f..526a8f911e 100644
--- a/addons/dark-www/banners/desaturated.css
+++ b/addons/dark-www/banners/desaturated.css
@@ -37,6 +37,7 @@
 .parents .title-banner.masthead .ted-talk {
   border-color: black;
 }
+.membership-page .get-involved-section,
 .educators .title-banner.masthead,
 .educators #teacher-accounts,
 .expect .keynote,
diff --git a/addons/dark-www/experimental_scratchwww.css b/addons/dark-www/experimental_scratchwww.css
index 573395fe9e..c9b22827f2 100644
--- a/addons/dark-www/experimental_scratchwww.css
+++ b/addons/dark-www/experimental_scratchwww.css
@@ -372,6 +372,7 @@ body:not(.sa-body-editor) .outer .sort-mode .select select:focus {
 /* Blue background */
 .empty,
 .intro-banner .intro-subnav,
+.membership-page .scratch-membership-section,
 .social-message.mod-unread,
 .preview .remix-credit,
 .preview .project-description,
diff --git a/addons/discuss-button/addon.json b/addons/discuss-button/addon.json
index 0e8b0f02ac..609f8ec823 100644
--- a/addons/discuss-button/addon.json
+++ b/addons/discuss-button/addon.json
@@ -3,17 +3,22 @@
   "description": "Choose a list of links to be displayed in the navigation bar.",
   "userscripts": [
     {
-      "url": "userscript.js",
-      "matches": ["https://scratch.mit.edu/*", "https://scratch.mit.edu/403", "https://scratch.mit.edu/404"],
+      "url": "items_scratchwww.js",
+      "matches": ["scratchWWWNoProject", "projects"],
       "runAtComplete": false
     },
     {
-      "url": "www.js",
+      "url": "items_scratchr2.js",
+      "matches": ["isNotScratchWWW", "https://scratch.mit.edu/403", "https://scratch.mit.edu/404"],
+      "runAtComplete": false
+    },
+    {
+      "url": "compact_scratchwww.js",
       "matches": ["scratchWWWNoProject", "projects"],
       "runAtComplete": false
     },
     {
-      "url": "r2.js",
+      "url": "compact_scratchr2.js",
       "matches": ["isNotScratchWWW", "https://scratch.mit.edu/403", "https://scratch.mit.edu/404"],
       "runAtComplete": false
     }
@@ -46,8 +51,7 @@
       "default": [
         { "name": "Create", "url": "/projects/editor/" },
         { "name": "Explore", "url": "/explore/projects/all" },
-        { "name": "Ideas", "url": "/ideas" },
-        { "name": "About", "url": "/about" }
+        { "name": "Ideas", "url": "/ideas" }
       ],
       "row": [
         {
@@ -90,6 +94,12 @@
         }
       ]
     },
+    {
+      "name": "Show Membership link when logged out",
+      "id": "showMembership",
+      "type": "boolean",
+      "default": true
+    },
     {
       "name": "Compact user dropdown",
       "id": "compact-nav",
diff --git a/addons/discuss-button/r2.js b/addons/discuss-button/compact_scratchr2.js
similarity index 100%
rename from addons/discuss-button/r2.js
rename to addons/discuss-button/compact_scratchr2.js
diff --git a/addons/discuss-button/www.js b/addons/discuss-button/compact_scratchwww.js
similarity index 100%
rename from addons/discuss-button/www.js
rename to addons/discuss-button/compact_scratchwww.js
diff --git a/addons/discuss-button/items_scratchr2.js b/addons/discuss-button/items_scratchr2.js
new file mode 100644
index 0000000000..31f8267917
--- /dev/null
+++ b/addons/discuss-button/items_scratchr2.js
@@ -0,0 +1,59 @@
+export default async function ({ addon, console, msg }) {
+  let originalNavbar = [];
+  await addon.tab.waitForElement(".search", { markAsSeen: true });
+  const list = document.querySelector(".site-nav");
+
+  function createItem({ name, url }, last) {
+    const li = document.createElement("li");
+    li.className = "link";
+    if (last) li.classList.add("last");
+
+    const a = document.createElement("a");
+    const absolute = new URL(url, location.origin);
+    a.href = ["http:", "https:"].includes(absolute.protocol) ? absolute.toString() : "";
+    li.append(a);
+    // scratch's code looks for this id in account-nav.js
+    a.id = "project-create";
+
+    const span = document.createElement("span");
+    span.innerText = name;
+    a.append(span);
+
+    return li;
+  }
+  function removeAllItems() {
+    if (originalNavbar.length === 0) {
+      originalNavbar.push(
+        ...Array.prototype.map.call(list.children, (item) => ({
+          name: item.innerText,
+          url: item.firstChild.href,
+        }))
+      );
+    }
+    while (list.firstChild) {
+      list.removeChild(list.lastChild);
+    }
+    return;
+  }
+  async function init() {
+    const loggedIn = await addon.auth.fetchIsLoggedIn();
+    removeAllItems();
+    let items = addon.self.disabled ? originalNavbar : addon.settings.get("items");
+    if (!addon.self.disabled && !loggedIn && addon.settings.get("showMembership")) {
+      items = [
+        ...items,
+        {
+          name: msg("membership"),
+          url: "/membership",
+        },
+      ];
+    }
+    items.forEach((item, i) => {
+      list.append(createItem(item, i + 1 === items.length));
+    });
+  }
+  init();
+  addon.settings.addEventListener("change", init);
+  addon.self.addEventListener("disabled", init);
+  addon.self.addEventListener("reenabled", init);
+}
diff --git a/addons/discuss-button/items_scratchwww.js b/addons/discuss-button/items_scratchwww.js
new file mode 100644
index 0000000000..a6181a3327
--- /dev/null
+++ b/addons/discuss-button/items_scratchwww.js
@@ -0,0 +1,106 @@
+const REACT_ELEMENT = Symbol.for("react.element");
+
+export default async function ({ addon, console }) {
+  const createReactElement = (type, props, ...children) => {
+    const key = props.key ?? null;
+    const ref = props.ref ?? null;
+    delete props.key;
+    delete props.ref;
+    if (type.defaultProps) {
+      props = Object.assign({}, type.defaultProps, props);
+    }
+    if (children.length > 1) props.children = children;
+    else if (children.length === 1) props.children = children[0];
+    return {
+      $$typeof: REACT_ELEMENT,
+      type,
+      props,
+      key,
+      ref,
+    };
+  };
+
+  const navbar = await addon.tab.waitForElement("#navigation > .inner", {
+    markAsSeen: true,
+    reduxCondition: (state) => {
+      if (!state.scratchGui) return true;
+      return state.scratchGui.mode.isPlayerOnly;
+    },
+  });
+  let fiberNode = navbar[addon.tab.traps.getInternalKey(navbar)];
+  while (!fiberNode.stateNode?.handleSearchSubmit) {
+    fiberNode = fiberNode.return;
+  }
+  const navigationInstance = fiberNode.stateNode;
+  const Navigation = navigationInstance.constructor;
+
+  const oldRender = Navigation.prototype.render;
+  Navigation.prototype.render = function () {
+    if (addon.self.disabled) return oldRender.call(this);
+
+    // The objects returned by oldRender() are immutable in the development version
+    // of React, but overriding Object.freeze() allows us to change them. This won't
+    // cause problems because React hasn't seen the objects yet at this point.
+    const oldFreeze = Object.freeze;
+    Object.freeze = () => {};
+    const result = oldRender.call(this);
+    Object.freeze = oldFreeze;
+
+    const list = result.props.children[0];
+    if (list.type !== "ul") return result;
+
+    let items = addon.settings.get("items");
+    const loggedIn = !!this.props.user;
+    if (!loggedIn && addon.settings.get("showMembership")) {
+      items = [
+        ...items,
+        {
+          name: addon.tab.scratchMessage("general.membership"),
+          url: "/membership",
+        },
+      ];
+    }
+
+    list.props.children = [
+      list.props.children[0], // logo
+
+      ...items.map(({ name, url }) => {
+        const absolute = new URL(url, location.origin);
+        return createReactElement(
+          "li",
+          { className: "link" },
+          createReactElement(
+            "a",
+            { href: ["http:", "https:"].includes(absolute.protocol) ? absolute.toString() : "" },
+            createReactElement("span", {}, name)
+          )
+        );
+      }),
+
+      ...list.props.children.slice(1).filter(
+        // remove original links
+        (child) =>
+          !(
+            child &&
+            child.type === "li" &&
+            child.props.className.includes("link") &&
+            !child.props.className.includes("right")
+          )
+      ),
+    ];
+    return result;
+  };
+  navigationInstance.render = Navigation.prototype.render.bind(navigationInstance);
+
+  const updateItems = () => {
+    // force rerender
+    addon.tab.redux.dispatch({
+      type: "SET_STATUS",
+      status: addon.tab.redux.state.session.status,
+    });
+  };
+  updateItems();
+  addon.settings.addEventListener("change", updateItems);
+  addon.self.addEventListener("disabled", updateItems);
+  addon.self.addEventListener("reenabled", updateItems);
+}
diff --git a/addons/discuss-button/userscript.js b/addons/discuss-button/userscript.js
deleted file mode 100644
index 82b0f3522c..0000000000
--- a/addons/discuss-button/userscript.js
+++ /dev/null
@@ -1,83 +0,0 @@
-export default async function ({ addon, console }) {
-  let originalNavbar = [];
-  while (true) {
-    const searchItem = await addon.tab.waitForElement(".search", {
-      markAsSeen: true,
-      reduxCondition: (state) => {
-        if (!state.scratchGui) return true;
-        return state.scratchGui.mode.isPlayerOnly;
-      },
-    });
-    const scratchr2List = document.querySelector(".site-nav");
-
-    function createItem({ name, url, extraClass }, last) {
-      const li = document.createElement("li");
-      li.className = "link";
-      if (last) li.classList.add("last");
-      if (addon.tab.clientVersion !== "scratchr2" && typeof extraClass === "string") li.classList.add(extraClass);
-
-      const a = document.createElement("a");
-      const absolute = new URL(url, location.origin);
-      a.href = ["http:", "https:"].includes(absolute.protocol) ? absolute.toString() : "";
-      li.append(a);
-      if (scratchr2List) {
-        // scratch's code looks for this id in account-nav.js (scratchr2 only).
-        a.id = "project-create";
-      }
-
-      const span = document.createElement("span");
-      span.innerText = name;
-      a.append(span);
-
-      return li;
-    }
-    function removeAllItems() {
-      if (scratchr2List) {
-        // We are on scratchr2!
-        if (originalNavbar.length < 4) {
-          originalNavbar.push(
-            ...Array.prototype.map.call(scratchr2List.children, (item) => ({
-              name: item.innerText,
-              url: item.firstChild.href,
-            }))
-          );
-        }
-        while (scratchr2List.firstChild) {
-          scratchr2List.removeChild(scratchr2List.lastChild);
-        }
-        return;
-      }
-      while (!searchItem.previousSibling.classList.contains("logo")) {
-        searchItem.previousSibling.remove();
-      }
-    }
-    function init() {
-      removeAllItems();
-      const items = addon.self.disabled
-        ? originalNavbar.length === 0
-          ? (originalNavbar = [
-              { name: addon.tab.scratchMessage("general.create"), url: "/projects/editor/", extraClass: "create" },
-              {
-                name: addon.tab.scratchMessage("general.explore"),
-                url: "/explore/projects/all",
-                extraClass: "explore",
-              },
-              { name: addon.tab.scratchMessage("general.ideas"), url: "/ideas", extraClass: "ideas" },
-              { name: addon.tab.scratchMessage("general.about"), url: "/about", extraClass: "about" },
-            ])
-          : originalNavbar
-        : addon.settings.get("items");
-      items.forEach((item, i) => {
-        if (scratchr2List) {
-          scratchr2List.append(createItem(item, i + 1 === items.length));
-          return;
-        }
-        searchItem.parentElement.insertBefore(createItem(item), searchItem);
-      });
-    }
-    init();
-    addon.settings.addEventListener("change", init);
-    addon.self.addEventListener("disabled", init);
-    addon.self.addEventListener("reenabled", init);
-  }
-}
diff --git a/addons/drag-drop/userscript.js b/addons/drag-drop/userscript.js
index bf5c5e9d5e..0a8cdaaacc 100644
--- a/addons/drag-drop/userscript.js
+++ b/addons/drag-drop/userscript.js
@@ -57,9 +57,9 @@ export default async function ({ addon, console }) {
     let el;
     let callback;
     if (
-      (el = e.target.closest('div[class*="sprite-selector_sprite-selector"]')) ||
-      (el = e.target.closest('div[class*="stage-selector_stage-selector"]')) ||
-      (el = e.target.closest('div[class*="selector_wrapper"]'))
+      (el = e.target.closest('[class*="sprite-selector_sprite-selector"]')) ||
+      (el = e.target.closest('[class*="stage-selector_stage-selector"]')) ||
+      (el = e.target.closest('[class*="selector_wrapper_"]'))
     ) {
       callback = (files) => {
         const hdFilter = addon.settings.get("use-hd-upload") ? "" : ":not(.sa-better-img-uploads-input)";
@@ -114,9 +114,7 @@ export default async function ({ addon, console }) {
         // Simulate clicking on the "Import" option
         contextMenu.children[0].click();
       };
-    } else if (
-      (el = e.target.closest('div[class*="question_question-input"] > input[class*="input_input-form_l9eYg"]'))
-    ) {
+    } else if ((el = e.target.closest('[class*="question_question-input"] > [class*="input_input-form_"]'))) {
       callback = async (files) => {
         const text = (await Promise.all(Array.from(files, (file) => file.text())))
           .join("")
diff --git a/addons/editor-buttons-reverse-order/userstyle.css b/addons/editor-buttons-reverse-order/userstyle.css
index 4fac92154c..27128324d4 100644
--- a/addons/editor-buttons-reverse-order/userstyle.css
+++ b/addons/editor-buttons-reverse-order/userstyle.css
@@ -20,7 +20,7 @@
   margin-right: 0.2rem;
 }
 
-[class*="green-flag_green-flag_"] {
+[class*="green-flag_green-flag-button_"] {
   order: -1;
 }
 
@@ -28,7 +28,7 @@
   order: -2;
 }
 
-[class*="stop-all_stop-all_"] {
+[class*="stop-all_stop-all-button_"] {
   order: -3;
 }
 
diff --git a/addons/editor-dark-mode/zoom_icons.js b/addons/editor-dark-mode/zoom_icons.js
index 4eee498e41..e3f52f5550 100644
--- a/addons/editor-dark-mode/zoom_icons.js
+++ b/addons/editor-dark-mode/zoom_icons.js
@@ -36,7 +36,8 @@ export default async function ({ addon, console }) {
       reduxEvents: [
         "scratch-gui/mode/SET_PLAYER",
         "scratch-gui/locales/SELECT_LOCALE",
-        "scratch-gui/theme/SET_THEME",
+        "scratch-gui/settings/SET_COLOR_MODE",
+        "scratch-gui/settings/SET_THEME",
         "fontsLoaded/SET_FONTS_LOADED",
       ],
       reduxCondition: (state) => state.scratchGui.editorTab.activeTabIndex === 0 && !state.scratchGui.mode.isPlayerOnly,
diff --git a/addons/editor-stage-left/stageleft.css b/addons/editor-stage-left/stageleft.css
index 7fd8a6b233..22a13b7bf7 100644
--- a/addons/editor-stage-left/stageleft.css
+++ b/addons/editor-stage-left/stageleft.css
@@ -23,7 +23,7 @@
   margin-right: calc(0.5rem / 2);
   margin-left: 0;
 }
-[class^="gui_flex-wrapper"] {
+[class*="gui_flex-wrapper_"] {
   flex-direction: row-reverse;
   overflow-x: hidden;
 }
diff --git a/addons/editor-theme3/theme3.js b/addons/editor-theme3/theme3.js
index 85cf0f9766..72ebda2b26 100644
--- a/addons/editor-theme3/theme3.js
+++ b/addons/editor-theme3/theme3.js
@@ -237,7 +237,8 @@ export default async function ({ addon, console, msg }) {
         "scratch-gui/mode/SET_PLAYER",
         "fontsLoaded/SET_FONTS_LOADED",
         "scratch-gui/locales/SELECT_LOCALE",
-        "scratch-gui/theme/SET_THEME",
+        "scratch-gui/settings/SET_COLOR_MODE",
+        "scratch-gui/settings/SET_THEME",
         "scratch-gui/monitors/UPDATE_MONITORS",
       ].includes(e.detail.action.type)
     ) {
diff --git a/addons/gamepad/gamepadlib.js b/addons/gamepad/gamepadlib.js
index bc2732ed0d..6a844da41f 100644
--- a/addons/gamepad/gamepadlib.js
+++ b/addons/gamepad/gamepadlib.js
@@ -1,3 +1,5 @@
+import { isFirefox } from "../../libraries/common/cs/detect-browser.js";
+
 let console = window.console;
 
 /*
@@ -652,7 +654,7 @@ GamepadLib.browserHasBrokenGamepadAPI = () => {
   // Firefox on Linux before version 123 has a broken gamepad API that results in strange and unusable mappings
   // https://bugzilla.mozilla.org/show_bug.cgi?id=1680982
   // https://bugzilla.mozilla.org/show_bug.cgi?id=1643835
-  if (navigator.userAgent.includes("Firefox") && navigator.userAgent.includes("Linux")) {
+  if (isFirefox() && navigator.userAgent.includes("Linux")) {
     const agentMatch = navigator.userAgent.match(/Firefox\/(\d+)/);
     // If we couldn't find the version number, we'll assume that this is some distant future version of
     // Firefox that we just can't comprehend with the technology of today. Surely gamepad will work well
@@ -662,7 +664,7 @@ GamepadLib.browserHasBrokenGamepadAPI = () => {
   }
   // Firefox on macOS has other bugs that result in strange and unusable mappings
   // eg. https://bugzilla.mozilla.org/show_bug.cgi?id=1434408
-  if (navigator.userAgent.includes("Firefox") && navigator.userAgent.includes("Mac OS")) {
+  if (isFirefox() && navigator.userAgent.includes("Mac OS")) {
     return true;
   }
   return false;
diff --git a/addons/hide-backpack/userscript.js b/addons/hide-backpack/userscript.js
index be27bcf749..ce552316b1 100644
--- a/addons/hide-backpack/userscript.js
+++ b/addons/hide-backpack/userscript.js
@@ -11,7 +11,10 @@ export default async function ({ addon, console }) {
 
   addon.tab.redux.initialize();
   addon.tab.redux.addEventListener("statechanged", (e) => {
-    if (e.detail.action.type === "scratch-gui/theme/SET_THEME" && !addon.self.disabled) {
+    if (
+      ["scratch-gui/settings/SET_COLOR_MODE", "scratch-gui/settings/SET_THEME"].includes(e.detail.action.type) &&
+      !addon.self.disabled
+    ) {
       // queueMicrotask isn't enough on new Blockly
       setTimeout(changeBackpackVisibility, 0);
     }
diff --git a/addons/hide-delete-button/costumes.css b/addons/hide-delete-button/costumes.css
index eedb08f8f5..7b0d6a43e1 100644
--- a/addons/hide-delete-button/costumes.css
+++ b/addons/hide-delete-button/costumes.css
@@ -1,3 +1,3 @@
-[class*="gui_tabs_"] > :nth-child(3) div[class*="delete-button_delete-button_"] {
+[class*="gui_tabs_"] > :nth-child(3) [class*="delete-button_delete-button_"] {
   display: none;
 }
diff --git a/addons/hide-delete-button/show-trash-shortcut.css b/addons/hide-delete-button/show-trash-shortcut.css
index 7afcbeca6e..d27d515598 100644
--- a/addons/hide-delete-button/show-trash-shortcut.css
+++ b/addons/hide-delete-button/show-trash-shortcut.css
@@ -1,4 +1,4 @@
-.sa-show-trash div[class*="target-pane_target-pane_"]:hover div[class*="delete-button_delete-button_"],
-.sa-show-trash div[class*="selector_wrapper_"]:hover div[class*="delete-button_delete-button_"] {
+.sa-show-trash [class*="target-pane_target-pane_"]:hover [class*="delete-button_delete-button_"],
+.sa-show-trash [class*="selector_wrapper_"]:hover [class*="delete-button_delete-button_"] {
   display: block !important;
 }
diff --git a/addons/hide-delete-button/sounds.css b/addons/hide-delete-button/sounds.css
index 5ad00678ad..cc62b11380 100644
--- a/addons/hide-delete-button/sounds.css
+++ b/addons/hide-delete-button/sounds.css
@@ -1,3 +1,3 @@
-[class*="gui_tabs_"] > :nth-child(4) div[class*="delete-button_delete-button_"] {
+[class*="gui_tabs_"] > :nth-child(4) [class*="delete-button_delete-button_"] {
   display: none;
 }
diff --git a/addons/hide-delete-button/sprites.css b/addons/hide-delete-button/sprites.css
index 4a4d0fd299..b747c61d0f 100644
--- a/addons/hide-delete-button/sprites.css
+++ b/addons/hide-delete-button/sprites.css
@@ -1,3 +1,3 @@
-div[class*="sprite-selector_sprite-wrapper_"] div[class*="delete-button_delete-button_"] {
+[class*="sprite-selector_sprite-wrapper_"] [class*="delete-button_delete-button_"] {
   display: none;
 }
diff --git a/addons/hide-flyout/userscript.js b/addons/hide-flyout/userscript.js
index 73335e853a..f0e395f3db 100644
--- a/addons/hide-flyout/userscript.js
+++ b/addons/hide-flyout/userscript.js
@@ -359,7 +359,8 @@ export default async function ({ addon, console, msg }) {
       reduxEvents: [
         "scratch-gui/mode/SET_PLAYER",
         "scratch-gui/locales/SELECT_LOCALE",
-        "scratch-gui/theme/SET_THEME",
+        "scratch-gui/settings/SET_COLOR_MODE",
+        "scratch-gui/settings/SET_THEME",
         "fontsLoaded/SET_FONTS_LOADED",
       ],
       reduxCondition: (state) => !state.scratchGui.mode.isPlayerOnly,
diff --git a/addons/player-thumb/userscript.js b/addons/player-thumb/userscript.js
index 6421723d7f..02653d5834 100644
--- a/addons/player-thumb/userscript.js
+++ b/addons/player-thumb/userscript.js
@@ -7,7 +7,7 @@ export default async function ({ addon, console }) {
   thumb.classList = "sa-project-thumb loading";
   thumb.draggable = false;
 
-  const stageWrapper = await addon.tab.waitForElement('div[class*="stage-wrapper_stage-wrapper_"]');
+  const stageWrapper = await addon.tab.waitForElement('[class*="stage-wrapper_stage-wrapper_"]');
   addon.tab.redux.initialize();
 
   // It's possible this runs after the project loads even without dynamic enable
@@ -16,7 +16,7 @@ export default async function ({ addon, console }) {
   if (addon.tab.editorMode === "editor") return;
 
   const alerts = document.querySelector(".project-info-alerts");
-  const controls = stageWrapper.querySelector('div[class^="controls_controls-container_"]');
+  const controls = stageWrapper.querySelector('[class*="controls_controls-container_"]');
   controls.classList.add("sa-controls-disabled");
 
   const loaderBackground = stageWrapper.querySelector('[class*="loader_background_"]');
diff --git a/addons/scratch3to2/comments.css b/addons/scratch3to2/comments.css
index 3564ffa7b0..a1561f63a3 100644
--- a/addons/scratch3to2/comments.css
+++ b/addons/scratch3to2/comments.css
@@ -23,10 +23,13 @@
 .comments-root-reply:empty {
   padding: 0;
 }
-.comment .avatar {
+.comment .avatar-wrapper,
+.preview .comment .avatar-wrapper {
   margin-right: 10px;
-  width: 45px;
-  height: 45px;
+  --avatar-size: 45px;
+}
+.comment .avatar,
+.preview .comment img.avatar {
   border-radius: 0;
   box-shadow: none;
 }
diff --git a/addons/scratch3to2/explore_and_search.css b/addons/scratch3to2/explore_and_search.css
index e61d3529cc..1760435aa7 100644
--- a/addons/scratch3to2/explore_and_search.css
+++ b/addons/scratch3to2/explore_and_search.css
@@ -199,8 +199,7 @@ body:not(.sa-body-editor) .outer .sort-mode .select select {
   border-radius: 0;
 }
 .grid .thumbnail .thumbnail-info .creator-image img {
-  margin-left: -1px;
-  margin-right: 7px;
+  box-sizing: border-box;
   border: 1px solid var(--darkWww-border-15, #ddd);
   border-radius: 0;
 }
diff --git a/addons/scratch3to2/main.css b/addons/scratch3to2/main.css
index d14c278723..69b6faf602 100644
--- a/addons/scratch3to2/main.css
+++ b/addons/scratch3to2/main.css
@@ -320,6 +320,7 @@ body:not(.sa-body-editor) .select select > option {
   background-size: auto;
 }
 .account-nav .user-info {
+  display: inline-block;
   height: 35px;
   padding: 0 10px;
   background-clip: padding-box;
@@ -327,9 +328,14 @@ body:not(.sa-body-editor) .select select > option {
   border-right: 1px solid transparent;
   line-height: 35px;
 }
-.account-nav .user-info .avatar {
+.account-nav .user-info .avatar-wrapper {
+  vertical-align: middle;
   margin-top: -3px;
   margin-right: 5px;
+  --avatar-size: 26px;
+}
+.account-nav .user-info .avatar {
+  box-sizing: border-box;
   border: 1px solid #ccc;
   border-radius: 1px;
 }
diff --git a/addons/scratch3to2/project.css b/addons/scratch3to2/project.css
index 447d197953..66dcc4b412 100644
--- a/addons/scratch3to2/project.css
+++ b/addons/scratch3to2/project.css
@@ -48,8 +48,9 @@
 
 /* Title */
 .preview > .inner > .preview-row:first-child {
-  min-height: 45px;
-  padding: 7px 20px 2px;
+  min-height: 47px;
+  padding: 2px 20px;
+  align-items: center;
   background-color: var(--darkWww-gray-scratchr2, #f7f7f7);
   border-top: 1px solid var(--darkWww-gray-boxHighlight, white);
   border-bottom: 1px solid var(--darkWww-box-scratchr2Border, #e0e0e0);
@@ -57,10 +58,12 @@
   color: var(--darkWww-gray-scratchr2Text, #322f31);
   text-shadow: var(--darkWww-gray-scratchr2TextShadow, 0 1px white);
 }
-.preview .project-header img.avatar {
+.preview .project-header .avatar-wrapper {
   vertical-align: middle;
-  width: 40px;
-  height: 40px;
+  --avatar-size: 42px;
+}
+.preview .project-header img.avatar {
+  box-sizing: border-box;
   border: 1px solid var(--darkWww-border-15, #ccc);
   border-radius: 0;
 }
@@ -70,12 +73,14 @@
   line-height: 20px;
 }
 .preview .project-title {
-  margin-bottom: -3px;
   color: var(--darkWww-gray-scratchr2HeaderText, #554747);
   font-size: 22px;
   font-weight: bold;
   line-height: 26px;
 }
+.preview .project-title.no-edit {
+  margin-bottom: -3px;
+}
 .preview .project-header .inplace-input {
   height: 38px;
   padding: 0 10px;
@@ -110,7 +115,6 @@
 
 /* Remix, See inside, turbowarp-player */
 .preview .project-buttons {
-  margin-top: 2px;
   margin-right: -2px;
 }
 .preview .remix-button,
@@ -390,10 +394,12 @@ body:not(.sa-body-editor) [class*="stage_green-flag-overlay_"] > img {
   border-radius: 0;
   border-bottom: 1px solid var(--darkWww-border, #ddd);
 }
-.preview img.avatar.remix {
+.preview .remix-credit .avatar-wrapper {
   margin-right: 5px;
-  width: 30px;
-  height: 30px;
+  --avatar-size: 32px;
+}
+.preview img.avatar.remix {
+  box-sizing: border-box;
   border: 1px solid var(--darkWww-border-15, #ccc);
   border-radius: 0;
 }
@@ -781,11 +787,6 @@ body:not(.sa-body-editor) [class*="stage_green-flag-overlay_"] > img {
 .preview .comments-container .comments-allowed-input {
   margin-right: 0;
 }
-.preview .comment img.avatar {
-  width: 45px;
-  height: 45px;
-  border-radius: 0;
-}
 .compose-comment .compose-bottom-row .compose-limit {
   color: var(--darkWww-box-scratchr2ButtonText, #666);
 }
diff --git a/addons/scratch3to2/studio.css b/addons/scratch3to2/studio.css
index 899690e060..b3972976d8 100644
--- a/addons/scratch3to2/studio.css
+++ b/addons/scratch3to2/studio.css
@@ -289,6 +289,7 @@
   line-height: 0;
 }
 .studio-project-tile .studio-project-avatar {
+  box-sizing: border-box;
   border: 1px solid var(--darkWww-border-15, #ddd);
   border-radius: 0;
 }
@@ -336,6 +337,7 @@
   line-height: 0;
 }
 .studio-member-tile .studio-member-image {
+  box-sizing: border-box;
   border: 1px solid var(--darkWww-border-20, #ccc);
   border-radius: 0;
 }
diff --git a/addons/scratchr2/scratchr2.css b/addons/scratchr2/scratchr2.css
index 7c13a8a5c8..f20b751c31 100644
--- a/addons/scratchr2/scratchr2.css
+++ b/addons/scratchr2/scratchr2.css
@@ -311,6 +311,7 @@ select:focus {
   background-color: var(--darkWww-navbar-border, rgba(0, 0, 0, 0.1));
 }
 #topnav ul.site-nav li a {
+  vertical-align: middle;
   height: 33px;
   padding: 13px 15px 4px 15px;
   color: var(--darkWww-navbar-text, white);
diff --git a/addons/scratchr2/scratchr2_comments.css b/addons/scratchr2/scratchr2_comments.css
index f757cd0fa2..6ce3ab597d 100644
--- a/addons/scratchr2/scratchr2_comments.css
+++ b/addons/scratchr2/scratchr2_comments.css
@@ -58,6 +58,13 @@
 #comments .comment img.avatar {
   margin-right: 8px;
 }
+#comments .comment .avatar-badge-wrapper {
+  margin-right: 8px;
+}
+#comments .comment .avatar-wrapper:not(.avatar-badge-wrapper) {
+  float: none;
+  margin-right: 0;
+}
 #comments .comments .info,
 #comments .comments li ul li .comment .info {
   width: calc(100% - 54px);
diff --git a/addons/zebra-striping/userscript.js b/addons/zebra-striping/userscript.js
index 02b985c518..8c1f0e4287 100644
--- a/addons/zebra-striping/userscript.js
+++ b/addons/zebra-striping/userscript.js
@@ -74,7 +74,8 @@ export default async function ({ addon, msg, console }) {
         "scratch-gui/mode/SET_PLAYER",
         "fontsLoaded/SET_FONTS_LOADED",
         "scratch-gui/locales/SELECT_LOCALE",
-        "scratch-gui/theme/SET_THEME",
+        "scratch-gui/settings/SET_COLOR_MODE",
+        "scratch-gui/settings/SET_THEME",
       ],
       reduxCondition: (state) => !state.scratchGui.mode.isPlayerOnly,
     });
diff --git a/background/firefox-localhost-support.js b/background/firefox-localhost-support.js
index 4aca52db9c..e49ec2f13d 100644
--- a/background/firefox-localhost-support.js
+++ b/background/firefox-localhost-support.js
@@ -1,4 +1,6 @@
-if (typeof browser === "object" && chrome.scripting) {
+import { isFirefox } from "../libraries/common/cs/detect-browser.js";
+
+if (isFirefox() && chrome.scripting) {
   const manifest = chrome.runtime.getManifest();
   const manifestScripts = manifest.content_scripts.filter((script) =>
     script.matches.includes("http://localhost:8601/*")
diff --git a/background/get-addon-settings.js b/background/get-addon-settings.js
index 59ffe891e1..d8016ff0f8 100644
--- a/background/get-addon-settings.js
+++ b/background/get-addon-settings.js
@@ -10,6 +10,7 @@ import { onReady } from "./imports/on-ready.js";
  - editor-theme3 4 (last bumped in v1.39)
  - dark-www 7 (bumped twice in v1.34.0)
  - forum-quote-code-beautifier 1 (last bumped in v1.34)
+ - discuss-button 1 (last bumped in v1.44.3)
  */
 
 // The following three functions are helper functions for the setting migration code
@@ -744,6 +745,13 @@ chrome.storage.sync.get([...ADDON_SETTINGS_KEYS, "addonsEnabled"], (storageItems
             // Respect the value of enabledByDefault (by doing nothing)
           }
         }
+
+        if (addonId === "discuss-button" && (settings._version || 0) < 1) {
+          // Transition v1.44.2 to v1.44.3
+          if (settings.items) settings.items = settings.items.filter((i) => i.url !== "/about");
+          settings._version = 1;
+          madeAnyChanges = madeChangesToAddon = true;
+        }
       }
 
       if (addonsEnabled[addonId] === undefined) addonsEnabled[addonId] = !!manifest.enabledByDefault;
diff --git a/background/get-userscripts.js b/background/get-userscripts.js
index 17e133e993..b8be148fb0 100644
--- a/background/get-userscripts.js
+++ b/background/get-userscripts.js
@@ -347,7 +347,7 @@ const WELL_KNOWN_PATTERNS = {
   // scratch-www routes, not including project pages
   // Matches /projects (an error page) but not /projects/<id>
   scratchWWWNoProject:
-    /^\/(?:(?:about|annual-report(?:\/\d+)?|camp|conference\/20(?:1[79]|[2-9]\d|18(?:\/(?:[^\/]+\/details|expect|plan|schedule))?)|contact-us|code-of-ethics|credits|developers|DMCA|download(?:\/(?:scratch2|scratch-link))?|educators(?:\/(?:faq|register|waiting))?|explore\/(?:project|studio)s\/\w+(?:\/\w+)?|community_guidelines|faq|ideas|join|messages|parents|privacy_policy(?:\/apps?)?|research|scratch_1\.4|search\/(?:project|studio)s|starter-projects|classes\/(?:complete_registration|[^\/]+\/register\/[^\/]+)|signup\/[^\/]+|terms_of_use|wedo(?:-legacy)?|ev3|microbit|vernier|boost|studios\/\d*(?:\/(?:projects|comments|curators|activity))?|components|become-a-scratcher|projects|cookies|accounts\/bad-username)\/?)?$/,
+    /^\/(?:(?:about|annual-report(?:\/\d+)?|camp|conference\/20(?:1[79]|[2-9]\d|18(?:\/(?:[^\/]+\/details|expect|plan|schedule))?)|contact-us|code-of-ethics|credits|developers|DMCA|download(?:\/(?:scratch2|scratch-link))?|educators(?:\/(?:faq|register|waiting))?|explore\/(?:project|studio)s\/\w+(?:\/\w+)?|community_guidelines|faq|ideas|join|messages|parents|privacy_policy(?:\/apps?)?|research|scratch_1\.4|search\/(?:project|studio)s|starter-projects|classes\/(?:complete_registration|[^\/]+\/register\/[^\/]+)|signup\/[^\/]+|terms_of_use|wedo(?:-legacy)?|ev3|microbit|vernier|boost|studios\/\d*(?:\/(?:projects|comments|curators|activity))?|components|become-a-scratcher|projects|cookies|accounts\/bad-username|membership)\/?)?$/,
 };
 
 const WELL_KNOWN_MATCHERS = {
diff --git a/background/handle-auth.js b/background/handle-auth.js
index 0c0a55e523..64c50aa805 100644
--- a/background/handle-auth.js
+++ b/background/handle-auth.js
@@ -1,6 +1,7 @@
 import { startCache } from "./message-cache.js";
 import { openMessageCache } from "../libraries/common/message-cache.js";
 import { purgeDatabase } from "../addons/scratch-notifier/notifier.js";
+import { isFirefox } from "../libraries/common/cs/detect-browser.js";
 
 async function getDefaultStoreId() {
   const CHROME_DEFAULT = "0";
@@ -168,8 +169,7 @@ function notify(cookie) {
   if (cookie.name === "scratchlanguage") return;
   const storeId = cookie.storeId;
   const cond = {};
-  if (typeof browser === "object") {
-    // Firefox-exclusive.
+  if (isFirefox()) {
     cond.cookieStoreId = storeId;
   }
   // On Chrome this can cause unnecessary session re-fetch, but there should be
diff --git a/background/handle-clipboard.js b/background/handle-clipboard.js
index 35934660f0..9116d350f7 100644
--- a/background/handle-clipboard.js
+++ b/background/handle-clipboard.js
@@ -1,3 +1,5 @@
+import { isFirefox } from "../libraries/common/cs/detect-browser.js";
+
 const dataURLToArrayBuffer = function (dataURL) {
   const byteString = atob(dataURL.split(",")[1]);
   const arrayBuffer = new ArrayBuffer(byteString.length);
@@ -8,8 +10,7 @@ const dataURLToArrayBuffer = function (dataURL) {
   return arrayBuffer;
 };
 
-if (typeof browser !== "undefined") {
-  // Firefox
+if (isFirefox()) {
   browser.runtime.onMessage.addListener(function (request) {
     if (request.clipboardDataURL && browser && browser.clipboard && browser.clipboard.setImageData) {
       const arrayBuffer = dataURLToArrayBuffer(request.clipboardDataURL);
diff --git a/background/imports/util.js b/background/imports/util.js
index 766fa25aaa..a6e907b2b5 100644
--- a/background/imports/util.js
+++ b/background/imports/util.js
@@ -1,7 +1,8 @@
+import { isFirefox } from "../../libraries/common/cs/detect-browser.js";
+
 // REMINDER: update similar code at /webpages/settings/index.js
 const browserLevelPermissions = ["notifications"];
-if (typeof browser !== "undefined") {
-  // Firefox only
+if (isFirefox()) {
   if (typeof Clipboard.prototype.write !== "function") {
     // Firefox 109-126 only
     browserLevelPermissions.push("clipboardWrite");
diff --git a/libraries/common/cs/detect-browser.js b/libraries/common/cs/detect-browser.js
new file mode 100644
index 0000000000..b94b803747
--- /dev/null
+++ b/libraries/common/cs/detect-browser.js
@@ -0,0 +1,3 @@
+export function isFirefox() {
+  return typeof new Error().fileName !== "undefined";
+}
diff --git a/libraries/common/notification-util.js b/libraries/common/notification-util.js
index ac1ed8d289..69273ced45 100644
--- a/libraries/common/notification-util.js
+++ b/libraries/common/notification-util.js
@@ -1,3 +1,5 @@
+import { isFirefox } from "./cs/detect-browser.js";
+
 let id = 0;
 
 export default function create(opts) {
@@ -7,7 +9,7 @@ export default function create(opts) {
   if (scratchAddons.muted) return Promise.resolve(null);
   const notifId = `${opts.base}__${Date.now()}_${id++}`;
   let newOpts;
-  if (!/Chrom/.test(navigator.userAgent)) {
+  if (isFirefox()) {
     newOpts = JSON.parse(JSON.stringify(opts));
     // On Firefox, remove notification properties that throw.
     delete newOpts.buttons;
diff --git a/manifest.json b/manifest.json
index e939af5586..5929483e28 100644
--- a/manifest.json
+++ b/manifest.json
@@ -2,8 +2,8 @@
   "manifest_version": 3,
   "name": "__MSG_extensionName__",
   "description": "__MSG_extensionDescription__",
-  "version": "1.44.1",
-  "version_name": "1.44.1",
+  "version": "1.44.5",
+  "version_name": "1.44.5",
   "default_locale": "en",
   "background": {
     "service_worker": "background/background.js",
diff --git a/webpages/settings/index.js b/webpages/settings/index.js
index 6d350ee95c..64602ae406 100644
--- a/webpages/settings/index.js
+++ b/webpages/settings/index.js
@@ -9,6 +9,7 @@ import exampleManifest from "./data/example-manifest.js";
 import fuseOptions from "./data/fuse-options.js";
 import globalTheme from "../../libraries/common/global-theme.js";
 import { deserializeSettings, serializeSettings } from "./settings-utils.js";
+import { isFirefox } from "../../libraries/common/cs/detect-browser.js";
 
 let isIframe = false;
 if (window.parent !== window) {
@@ -63,8 +64,7 @@ let fuse;
 
   // REMINDER: update similar code at /background/imports/util.js
   const browserLevelPermissions = ["notifications"];
-  if (typeof browser !== "undefined") {
-    // Firefox only
+  if (isFirefox()) {
     if (typeof Clipboard.prototype.write !== "function") {
       // Firefox 109-126 only
       browserLevelPermissions.push("clipboardWrite");
@@ -384,8 +384,7 @@ let fuse;
       // Autofocus search bar in iframe mode for both browsers
       // autofocus attribute only works in Chrome for us, so
       // we also manually focus on Firefox, even in fullscreen
-      if (isIframe || typeof browser !== "undefined")
-        setTimeout(() => document.getElementById("searchBox")?.focus(), 0);
+      if (isIframe || isFirefox()) setTimeout(() => document.getElementById("searchBox")?.focus(), 0);
 
       const exampleAddonListItem = {
         // Need to specify all used properties for reactivity!