From d28e1c14c69002bd90eed5286df4761db185ef5c Mon Sep 17 00:00:00 2001
From: Ehsan Akhgari <ehsan@mozilla.com>
Date: Fri, 16 Nov 2018 21:42:02 +0000
Subject: [PATCH] Bug 1507689 - Fix an intermittent failure condition in
 test_WebExtensionContentScript.js which is turned into a perma-failure with
 the patch in bug 1504728 r=kmag

Differential Revision: https://phabricator.services.mozilla.com/D12093

--HG--
extra : moz-landing-system : lando
---
 .../test/xpcshell/test_WebExtensionContentScript.js    | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/toolkit/components/extensions/test/xpcshell/test_WebExtensionContentScript.js b/toolkit/components/extensions/test/xpcshell/test_WebExtensionContentScript.js
index 12b3c617c660..22051021f974 100644
--- a/toolkit/components/extensions/test/xpcshell/test_WebExtensionContentScript.js
+++ b/toolkit/components/extensions/test/xpcshell/test_WebExtensionContentScript.js
@@ -57,10 +57,12 @@ async function loadURL(url, {frameCount}) {
     }
   }
   function loadObserver(window) {
-    windows.set(window.location.href, window);
-    if (windows.size == frameCount) {
-      resolveLoad();
-    }
+    window.addEventListener("load", function onLoad() {
+      windows.set(window.location.href, window);
+      if (windows.size == frameCount) {
+        resolveLoad();
+      }
+    }, {once: true});
   }
 
   Services.obs.addObserver(requestObserver, "http-on-examine-response");