Bug 1955241 - Fix separator appearing at top of toolbar context menu with no items above it. r=nsharpley

Differential Revision: https://phabricator.services.mozilla.com/D266705

Author: ky-ler

browser/base/content/main-popupset.js

@@ -495,6 +495,9 @@ document.addEventListener(
           ToolbarContextMenu.updateDownloadsAlwaysOpenPanel(event.target);
           ToolbarContextMenu.updateExtensionsButtonContextMenu(event.target);
           ToolbarContextMenu.updateExtension(event.target);
+          // hideLeadingSeparatorIfNeeded must be called last after updating the menu items above,
+          // as they may change which items are visible.
+          ToolbarContextMenu.hideLeadingSeparatorIfNeeded(event.target);
           break;
         case "pageActionContextMenu":
           BrowserPageActions.onContextMenuShowing(event, event.target);

browser/components/customizableui/ToolbarContextMenu.sys.mjs

@@ -553,4 +553,30 @@ export var ToolbarContextMenu = {
     let id = this._getExtensionId(popup);
     await BrowserAddonUI.manageAddon(id, "browserAction");
   },
+
+  /**
+   * Hides the first visible menu separator if it would appear at the top of the
+   * toolbar context menu (i.e., when all preceding menu items are hidden). This
+   * prevents a separator from appearing at the top of the menu with no items above it.
+   *
+   * Fix for Bug 1955241.
+   *
+   * @param {Element} popup
+   *   The toolbar-context-menu element for a window.
+   */
+  hideLeadingSeparatorIfNeeded(popup) {
+    // Find the first non-hidden element in the menu
+    let firstVisibleElement = popup.firstElementChild;
+    while (firstVisibleElement && firstVisibleElement.hidden) {
+      firstVisibleElement = firstVisibleElement.nextElementSibling;
+    }
+
+    // If the first visible element is a separator, hide it
+    if (
+      firstVisibleElement &&
+      firstVisibleElement.localName === "menuseparator"
+    ) {
+      firstVisibleElement.hidden = true;
+    }
+  },
 };