Bug 1179998 - Fix intermittent browser_876926_customize_mode_wrapping.js failures by checking whether a window was closed before trying to update the FxA parts of the UI r=Gijs

browser/base/content/browser-fxaccounts.js

@@ -266,6 +266,11 @@ let gFxAccounts = {
     let signedInTooltiptext = this.panelUIStatus.getAttribute("signedinTooltiptext");
 
     let updateWithUserData = (userData) => {
+      // Window might have been closed while fetching data.
+      if (window.closed) {
+        return;
+      }
+
       // Reset the button to its original state.
       this.panelUILabel.setAttribute("label", defaultLabel);
       this.panelUIStatus.removeAttribute("tooltiptext");