diff --git a/browser/base/content/browser-pageActions.js b/browser/base/content/browser-pageActions.js
index 073404a8db2b..00ebd78ec4d9 100644
--- a/browser/base/content/browser-pageActions.js
+++ b/browser/base/content/browser-pageActions.js
@@ -96,6 +96,7 @@ var BrowserPageActions = {
     for (let action of urlbarActions) {
       this.placeActionInUrlbar(action);
     }
+    this._updateMainButtonAttributes();
   },
 
   /**
@@ -128,6 +129,7 @@ var BrowserPageActions = {
   placeAction(action) {
     this.placeActionInPanel(action);
     this.placeActionInUrlbar(action);
+    this._updateMainButtonAttributes();
   },
 
   /**
@@ -213,6 +215,13 @@ var BrowserPageActions = {
     }
   },
 
+  _updateMainButtonAttributes() {
+    this.mainButtonNode.toggleAttribute(
+      "multiple-children",
+      PageActions.actions.length > 1
+    );
+  },
+
   /**
    * Returns the node before which an action's node should be inserted.
    *
@@ -545,6 +554,7 @@ var BrowserPageActions = {
     this._removeActionFromPanel(action);
     this._removeActionFromUrlbar(action);
     action.onRemovedFromWindow(window);
+    this._updateMainButtonAttributes();
   },
 
   _removeActionFromUrlbar(action) {
diff --git a/browser/base/content/browser.css b/browser/base/content/browser.css
index 7164f9c575e0..3c0269001237 100644
--- a/browser/base/content/browser.css
+++ b/browser/base/content/browser.css
@@ -762,6 +762,15 @@ toolbar:not(#TabsToolbar) > #personal-bookmarks {
     display: none;
   }
 }
+
+@supports -moz-bool-pref("browser.proton.urlbar.enabled") {
+  /* The page actions menu is hidden by default, it is only shown in small
+     windows as the overflow target of multiple page action buttons */
+  #pageActionButton {
+    visibility: collapse;
+  }
+}
+
 /* 680px is just below half of popular 1366px wide screens, so when putting two
    browser windows next to each other on such a screen, they'll be above this
    threshold. */
@@ -769,9 +778,15 @@ toolbar:not(#TabsToolbar) > #personal-bookmarks {
   /* Page action buttons are duplicated in the page action menu so we can
      safely hide them in small windows. */
   #pageActionSeparator,
-  #pageActionButton ~ .urlbar-page-action {
+  #pageActionButton[multiple-children] ~ .urlbar-page-action {
     display: none;
   }
+
+  @supports -moz-bool-pref("browser.proton.urlbar.enabled") {
+    #pageActionButton[multiple-children] {
+      visibility: visible;
+    }
+  }
 }
 @media (max-width: 550px) {
   #urlbar-container {
diff --git a/browser/base/content/moz.build b/browser/base/content/moz.build
index fd21ea5dd94b..f495d12e5181 100644
--- a/browser/base/content/moz.build
+++ b/browser/base/content/moz.build
@@ -43,7 +43,7 @@ with Files("test/keyboard/**"):
 with Files("test/outOfProcess/**"):
     BUG_COMPONENT = ("Firefox", "General")
 
-with Files("test/pageActions/**"):
+with Files("test/pageActions*/**"):
     BUG_COMPONENT = ("Firefox", "Toolbars and Customization")
 
 with Files("test/pageinfo/**"):
diff --git a/browser/base/content/test/pageActions-proton/.eslintrc.js b/browser/base/content/test/pageActions-proton/.eslintrc.js
new file mode 100644
index 000000000000..1779fd7f1cf8
--- /dev/null
+++ b/browser/base/content/test/pageActions-proton/.eslintrc.js
@@ -0,0 +1,5 @@
+"use strict";
+
+module.exports = {
+  extends: ["plugin:mozilla/browser-test"],
+};
diff --git a/browser/base/content/test/pageActions-proton/browser.ini b/browser/base/content/test/pageActions-proton/browser.ini
new file mode 100644
index 000000000000..30dc7d771b71
--- /dev/null
+++ b/browser/base/content/test/pageActions-proton/browser.ini
@@ -0,0 +1,7 @@
+[DEFAULT]
+prefs =
+  browser.proton.urlbar.enabled=true
+support-files =
+  head.js
+
+[browser_PageActions_overflow.js]
diff --git a/browser/base/content/test/pageActions-proton/browser_PageActions_overflow.js b/browser/base/content/test/pageActions-proton/browser_PageActions_overflow.js
new file mode 100644
index 000000000000..02976e4c7b54
--- /dev/null
+++ b/browser/base/content/test/pageActions-proton/browser_PageActions_overflow.js
@@ -0,0 +1,90 @@
+/* Any copyright is dedicated to the Public Domain.
+ * https://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+add_task(async function init() {
+  // We use an extension that shows a page action so that we can test the
+  // "remove extension" item in the context menu.
+  let extension = ExtensionTestUtils.loadExtension({
+    manifest: {
+      name: "Test contextMenu",
+      page_action: { show_matches: ["<all_urls>"] },
+    },
+
+    useAddonManager: "temporary",
+  });
+
+  await extension.startup();
+  let actionId = ExtensionCommon.makeWidgetId(extension.id);
+
+  let win = await BrowserTestUtils.openNewBrowserWindow();
+  await SimpleTest.promiseFocus(win);
+  let originalWindowWidth = win.outerWidth;
+  Assert.greater(originalWindowWidth, 700, "window is bigger than 700px");
+  BrowserTestUtils.loadURI(win.gBrowser, "data:text/html,<h1>A Page</h1>");
+  await BrowserTestUtils.browserLoaded(win.gBrowser.selectedBrowser);
+
+  // The pageAction implementation enables the button at the next animation
+  // frame, so before we look for the button we should wait one animation frame
+  // as well.
+  await promiseAnimationFrame(win);
+
+  registerCleanupFunction(async () => {
+    win.resizeTo(originalWindowWidth, win.outerHeight);
+    await BrowserTestUtils.closeWindow(win);
+  });
+
+  info("Check page action buttons are visible, the meatball button is not");
+  let addonButton = win.BrowserPageActions.urlbarButtonNodeForActionID(
+    actionId
+  );
+  Assert.ok(BrowserTestUtils.is_visible(addonButton));
+  let starButton = win.BrowserPageActions.urlbarButtonNodeForActionID(
+    "bookmark"
+  );
+  Assert.ok(BrowserTestUtils.is_visible(starButton));
+  let meatballButton = win.document.getElementById("pageActionButton");
+  Assert.ok(!BrowserTestUtils.is_visible(meatballButton));
+
+  info(
+    "Shrink the window, check page action buttons are not visible, the meatball menu is visible"
+  );
+  await promiseStableResize(500, win);
+  Assert.ok(!BrowserTestUtils.is_visible(addonButton));
+  Assert.ok(!BrowserTestUtils.is_visible(starButton));
+  Assert.ok(BrowserTestUtils.is_visible(meatballButton));
+
+  info(
+    "Remove the extension, check the only page action button is visible, the meatball menu is not visible"
+  );
+  let promiseUninstalled = promiseAddonUninstalled(extension.id);
+  await extension.unload();
+  await promiseUninstalled;
+  Assert.ok(BrowserTestUtils.is_visible(starButton));
+  Assert.ok(!BrowserTestUtils.is_visible(meatballButton));
+  Assert.deepEqual(
+    win.BrowserPageActions.urlbarButtonNodeForActionID(actionId),
+    null
+  );
+});
+
+// TODO (Bug 1700780): Why is this necessary? Without this trick the test
+// fails intermittently on Ubuntu.
+function promiseStableResize(expectedWidth, win = window) {
+  let deferred = PromiseUtils.defer();
+  let id;
+  function listener() {
+    win.clearTimeout(id);
+    info(`Got resize event: ${win.innerWidth} x ${win.innerHeight}`);
+    if (win.innerWidth <= expectedWidth) {
+      id = win.setTimeout(() => {
+        win.removeEventListener("resize", listener);
+        deferred.resolve();
+      }, 100);
+    }
+  }
+  win.addEventListener("resize", listener);
+  win.resizeTo(expectedWidth, win.outerHeight);
+  return deferred.promise;
+}
diff --git a/browser/base/content/test/pageActions-proton/head.js b/browser/base/content/test/pageActions-proton/head.js
new file mode 100644
index 000000000000..a2c012e88bad
--- /dev/null
+++ b/browser/base/content/test/pageActions-proton/head.js
@@ -0,0 +1,166 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+XPCOMUtils.defineLazyModuleGetters(this, {
+  ExtensionCommon: "resource://gre/modules/ExtensionCommon.jsm",
+  PlacesTestUtils: "resource://testing-common/PlacesTestUtils.jsm",
+});
+
+function promisePageActionPanelOpen(eventDict = {}) {
+  let dwu = window.windowUtils;
+  return BrowserTestUtils.waitForCondition(() => {
+    // Wait for the main page action button to become visible.  It's hidden for
+    // some URIs, so depending on when this is called, it may not yet be quite
+    // visible.  It's up to the caller to make sure it will be visible.
+    info("Waiting for main page action button to have non-0 size");
+    let bounds = dwu.getBoundsWithoutFlushing(
+      BrowserPageActions.mainButtonNode
+    );
+    return bounds.width > 0 && bounds.height > 0;
+  })
+    .then(() => {
+      // Wait for the panel to become open, by clicking the button if necessary.
+      info("Waiting for main page action panel to be open");
+      if (BrowserPageActions.panelNode.state == "open") {
+        return Promise.resolve();
+      }
+      let shownPromise = promisePageActionPanelShown();
+      EventUtils.synthesizeMouseAtCenter(
+        BrowserPageActions.mainButtonNode,
+        eventDict
+      );
+      return shownPromise;
+    })
+    .then(() => {
+      // Wait for items in the panel to become visible.
+      return promisePageActionViewChildrenVisible(
+        BrowserPageActions.mainViewNode
+      );
+    });
+}
+
+async function waitForActivatedActionPanel() {
+  if (!BrowserPageActions.activatedActionPanelNode) {
+    info("Waiting for activated-action panel to be added to mainPopupSet");
+    await new Promise(resolve => {
+      let observer = new MutationObserver(mutations => {
+        if (BrowserPageActions.activatedActionPanelNode) {
+          observer.disconnect();
+          resolve();
+        }
+      });
+      let popupSet = document.getElementById("mainPopupSet");
+      observer.observe(popupSet, { childList: true });
+    });
+    info("Activated-action panel added to mainPopupSet");
+  }
+  if (!BrowserPageActions.activatedActionPanelNode.state == "open") {
+    info("Waiting for activated-action panel popupshown");
+    await promisePanelShown(BrowserPageActions.activatedActionPanelNode);
+    info("Got activated-action panel popupshown");
+  }
+  let panelView = BrowserPageActions.activatedActionPanelNode.querySelector(
+    "panelview"
+  );
+  if (panelView) {
+    await BrowserTestUtils.waitForEvent(
+      BrowserPageActions.activatedActionPanelNode,
+      "ViewShown"
+    );
+    await promisePageActionViewChildrenVisible(panelView);
+  }
+  return panelView;
+}
+
+function promisePageActionPanelShown() {
+  return promisePanelShown(BrowserPageActions.panelNode);
+}
+
+function promisePageActionPanelHidden() {
+  return promisePanelHidden(BrowserPageActions.panelNode);
+}
+
+function promisePanelShown(panelIDOrNode) {
+  return promisePanelEvent(panelIDOrNode, "popupshown");
+}
+
+function promisePanelHidden(panelIDOrNode) {
+  return promisePanelEvent(panelIDOrNode, "popuphidden");
+}
+
+function promisePanelEvent(panelIDOrNode, eventType) {
+  return new Promise(resolve => {
+    let panel = panelIDOrNode;
+    if (typeof panel == "string") {
+      panel = document.getElementById(panelIDOrNode);
+      if (!panel) {
+        throw new Error(`Panel with ID "${panelIDOrNode}" does not exist.`);
+      }
+    }
+    if (
+      (eventType == "popupshown" && panel.state == "open") ||
+      (eventType == "popuphidden" && panel.state == "closed")
+    ) {
+      executeSoon(resolve);
+      return;
+    }
+    panel.addEventListener(
+      eventType,
+      () => {
+        executeSoon(resolve);
+      },
+      { once: true }
+    );
+  });
+}
+
+function promisePageActionViewShown() {
+  info("promisePageActionViewShown waiting for ViewShown");
+  return BrowserTestUtils.waitForEvent(
+    BrowserPageActions.panelNode,
+    "ViewShown"
+  ).then(async event => {
+    let panelViewNode = event.originalTarget;
+    await promisePageActionViewChildrenVisible(panelViewNode);
+    return panelViewNode;
+  });
+}
+
+function promisePageActionViewChildrenVisible(panelViewNode) {
+  return promiseNodeVisible(panelViewNode.firstElementChild.firstElementChild);
+}
+
+function promiseNodeVisible(node) {
+  info(
+    `promiseNodeVisible waiting, node.id=${node.id} node.localeName=${node.localName}\n`
+  );
+  let dwu = window.windowUtils;
+  return BrowserTestUtils.waitForCondition(() => {
+    let bounds = dwu.getBoundsWithoutFlushing(node);
+    if (bounds.width > 0 && bounds.height > 0) {
+      info(
+        `promiseNodeVisible OK, node.id=${node.id} node.localeName=${node.localName}\n`
+      );
+      return true;
+    }
+    return false;
+  });
+}
+
+function promiseAddonUninstalled(addonId) {
+  return new Promise(resolve => {
+    let listener = {};
+    listener.onUninstalled = addon => {
+      if (addon.id == addonId) {
+        AddonManager.removeAddonListener(listener);
+        resolve();
+      }
+    };
+    AddonManager.addAddonListener(listener);
+  });
+}
+
+async function promiseAnimationFrame(win = window) {
+  await new Promise(resolve => win.requestAnimationFrame(resolve));
+  await win.promiseDocumentFlushed(() => {});
+}
diff --git a/browser/base/moz.build b/browser/base/moz.build
index c97c964da0e6..2df182d913c6 100644
--- a/browser/base/moz.build
+++ b/browser/base/moz.build
@@ -33,6 +33,7 @@ BROWSER_CHROME_MANIFESTS += [
     "content/test/menubar/browser.ini",
     "content/test/metaTags/browser.ini",
     "content/test/outOfProcess/browser.ini",
+    "content/test/pageActions-proton/browser.ini",
     "content/test/pageActions/browser.ini",
     "content/test/pageinfo/browser.ini",
     "content/test/pageStyle/browser.ini",