https://treeherder.mozilla.org/logviewer.html#?job_id=77247852&repo=mozilla-inbound [task 2017-02-14T16:57:35.510240Z] 16:57:35 INFO - Console message: [JavaScript Error: "head is null" {file: "chrome://mochitests/content/browser/browser/base/content/test/general/browser_discovery.js" line: 70}] [task 2017-02-14T16:57:35.512218Z] 16:57:35 INFO - iconDiscovery@chrome://mochitests/content/browser/browser/base/content/test/general/browser_discovery.js:70:5 [task 2017-02-14T16:57:35.514292Z] 16:57:35 INFO - test/<@chrome://mochitests/content/browser/browser/base/content/test/general/browser_discovery.js:19:5 [task 2017-02-14T16:57:35.520543Z] 16:57:35 INFO - selfRemovingListener@resource://gre/modules/RemoteAddonsParent.jsm:607:7 [task 2017-02-14T16:57:35.522452Z] 16:57:35 INFO - dispatch/<@resource://gre/modules/RemoteAddonsParent.jsm:581:15 [task 2017-02-14T16:57:35.524358Z] 16:57:35 INFO - withPrefetching@resource://gre/modules/Prefetcher.jsm:443:14 [task 2017-02-14T16:57:35.526283Z] 16:57:35 INFO - dispatch@resource://gre/modules/RemoteAddonsParent.jsm:577:11 [task 2017-02-14T16:57:35.528265Z] 16:57:35 INFO - receiveMessage@resource://gre/modules/RemoteAddonsParent.jsm:525:9 [task 2017-02-14T16:57:35.532632Z] 16:57:35 INFO - [task 2017-02-14T16:57:35.535196Z] 16:57:35 INFO - Buffered messages finished [task 2017-02-14T16:57:35.537224Z] 16:57:35 INFO - TEST-UNEXPECTED-FAIL | browser/base/content/test/general/browser_discovery.js | Test timed out -

off-hand looks like this test is using cpows (browser.contentDocument) and not doing a great async management. Regardless, not a Location Bar test.

This could be fixed now by the changed in bug 1401777, let's tentatively mark it as such.