The following failure is causing a timeout of 370s for Mochitests:

https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=245035350&repo=autoland&lineNumber=915

03:14:04 INFO - runtests.py | Waiting for browser...
03:14:04 INFO - GECKO(1980) | 1557198844619 Marionette DEBUG Closed connection 1
03:14:04 INFO - GECKO(1980) | JavaScript error: chrome://mochikit/content/browser-test.js, line 90: TypeError: content is null
03:14:15 INFO - GECKO(1980) | 2019-05-07 03:14:15.590 firefox[1980:8015] Persistent UI failed to open file file:///Users/cltbld/Library/Saved%20Application%20State/org.mozilla.nightly.savedState/window_1.data: No such file or directory (2)
03:20:25 INFO - Buffered messages finished

Geoff, I think there are two problems here:

1. Javascript errors shouldn't end-up in the log as INFO but ERROR when it is related to the test harness.

2. The mochikit extension should be more robust for such a failure. In this case it's just for loading a URL, which completely freezes the extension:

https://searchfox.org/mozilla-central/rev/99a2a5a955960b0e58ceade1db1f7652d9db4ba1/testing/mochitest/browser-test.js#90-95

(In reply to Henrik Skupin (:whimboo) [⌚️UTC+1] from comment #0)

1. Javascript errors shouldn't end-up in the log as INFO but ERROR when it is related to the test harness.

Those errors will originate in Firefox, where they will probably be "logged" with dump() or similar. I suppose some logging code could search for strings like "Javascript error" and modify the logging level, but I don't know where to do that, and it seems potentially expensive in aggregate.

2. The mochikit extension should be more robust for such a failure. In this case it's just for loading a URL, which completely freezes the extension:

That would be good! I think usually, loads in harness code are essential. Retry failed loads? Or exit the browser immediately, to avoid the timeout??

It looks like this failure was introduced by bug 1546544, and resolved by its backout:

https://treeherder.mozilla.org/#/jobs?repo=mozilla-beta&searchStr=osx%2Cmochitest-chrome&tochange=21ec21b79d7721d59a63795c6c50f28690520a35&fromchange=0deba92b39fd52160009e0296dd096c18f33830f&selectedJob=245030180

If it fails to load an essential URL I think we should just fail and exit the browser.

The priority flag is not set for this bug.
:ahal, could you have a look please?

For more information, please visit auto_nag documentation.

Hm, could this failure maybe be related to bug 1553748?