Bug 1713120 - Fix TypeError: n.getAttribute is not a function in ext-pageAction.js r=rpl

The reported error happens because `.parentNode` can be a document,
which doesn't implement the Element interface. Using `.parentElement`
solves this issue.

And while I'm fixing this: move the logic behind the menu ID check, so
that the logic is not unnecessarily run for non-pageAction contextmenus.

Differential Revision: https://phabricator.services.mozilla.com/D116138

browser/components/extensions/parent/ext-pageAction.js

@@ -252,14 +252,17 @@ this.pageAction = class extends ExtensionAPI {
       case "popupshowing":
         const menu = event.target;
         const trigger = menu.triggerNode;
-        let actionId = trigger?.getAttribute("actionid");
-        if (trigger && !actionId) {
+        const getActionId = () => {
+          let actionId = trigger.getAttribute("actionid");
+          if (actionId) {
+            return actionId;
+          }
           // When a page action is clicked, triggerNode will be an ancestor of
           // a node corresponding to an action. triggerNode will be the page
           // action node itself when a page action is selected with the
           // keyboard. That's because the semantic meaning of page action is on
           // an hbox that contains an <image>.
-          for (let n = trigger.parentNode; n && !actionId; n = n.parentNode) {
+          for (let n = trigger; n && !actionId; n = n.parentElement) {
             if (n.id == "page-action-buttons" || n.localName == "panelview") {
               // We reached the page-action-buttons or panelview container.
               // Stop looking; no action was found.
@@ -267,11 +270,12 @@ this.pageAction = class extends ExtensionAPI {
             }
             actionId = n.getAttribute("actionid");
           }
-        }
+          return actionId;
+        };
         if (
           menu.id === "pageActionContextMenu" &&
           trigger &&
-          actionId === this.browserPageAction.id &&
+          getActionId() === this.browserPageAction.id &&
           !this.browserPageAction.getDisabled(trigger.ownerGlobal)
         ) {
           global.actionContextMenu({