--- a/browser/base/content/browser-pageActions.js
+++ b/browser/base/content/browser-pageActions.js
@@ -355,17 +355,24 @@ var BrowserPageActions = {
     buttonNode.addEventListener("contextmenu", event => {
       BrowserPageActions.onContextMenu(event);
     });
     if (action.nodeAttributes) {
       for (let name in action.nodeAttributes) {
         buttonNode.setAttribute(name, action.nodeAttributes[name]);
       }
     }
-    buttonNode.addEventListener("click", event => {
+
+    // The `activationEvent` should be `mousedown` if the only
+    // result of the click is the opening of a submenu.
+    //
+    // If the button has an additional action, this code will need to
+    // get additional parameter to recognize which event to use.
+    const activationEvent = action.subview ? "mousedown" : "click";
+    buttonNode.addEventListener(activationEvent, event => {
       if (event.button != 0) {
         return;
       }
       if (action.subview || action.wantsIframe) {
         this._toggleActivatedActionPanelForAction(action);
         return;
       }
       action.onCommand(event, buttonNode);