--- a/toolkit/components/extensions/test/mochitest/head_webrequest.js
+++ b/toolkit/components/extensions/test/mochitest/head_webrequest.js
@@ -183,16 +183,19 @@ function background(events) {
           browser.test.assertEq(expected.test.requestId, details.requestId, "redirects will keep the same requestId");
         } else {
           // Save any values we want to validate in later events.
           expected.test.requestId = details.requestId;
           expected.test.tabId = details.tabId;
         }
         // Tests we don't need to do every event.
         browser.test.assertTrue(details.type.toUpperCase() in browser.webRequest.ResourceType, `valid resource type ${details.type}`);
+        if (details.type == "main_frame") {
+          browser.test.assertEq(0, details.frameId, "frameId is zero when type is main_frame bug 1329299");
+        }
       } else {
         // On events after onBeforeRequest, check the previous values.
         browser.test.assertEq(expected.test.requestId, details.requestId, "correct requestId");
         browser.test.assertEq(expected.test.tabId, details.tabId, "correct tabId");
       }
       if (name == "onBeforeSendHeaders") {
         if (expected.headers && expected.headers.request) {
           result.requestHeaders = processHeaders("request", expected, details);