+++ This bug was initially created as a clone of Bug #1411913 +++ The changes in bug 1411913 were not effective for reftests, and I have been wishing that they were...hoping that they might (sometimes?) shed light on bug 1418575.

The previous attempt doesn't usually do anything in continuous integration because the -marionette option is not specified when calling runreftest.py. I don't think there's any harm in turning on trace logging by default like this -- just a few more lines of logging. https://treeherder.mozilla.org/#/jobs?repo=try&revision=108e8dd3e0f0f9fb52ed82d0bc6c92b79298d08c

Comment on attachment 8946486 [details] [diff] [review] enable marionette trace logging for reftests Review of attachment 8946486 [details] [diff] [review]: ----------------------------------------------------------------- ::: layout/tools/reftest/runreftest.py @@ +335,5 @@ > prefs['marionette.defaultPrefs.port'] = int(port) > > + # Enable tracing output for detailed failures in case of > + # failing connection attempts, and hangs (bug 1397201) > + prefs['marionette.logging'] = "TRACE" A bit more context would have helped me here. So after taking a look into the current code, what is `options.marionette` used for? If it's really only for host and port, it should get a better name. Feel free to do that in a follow-up bug, but at least add a comment above line 333.

Comment on attachment 8946486 [details] [diff] [review] enable marionette trace logging for reftests Review of attachment 8946486 [details] [diff] [review]: ----------------------------------------------------------------- ::: layout/tools/reftest/runreftest.py @@ +335,5 @@ > prefs['marionette.defaultPrefs.port'] = int(port) > > + # Enable tracing output for detailed failures in case of > + # failing connection attempts, and hangs (bug 1397201) > + prefs['marionette.logging'] = "TRACE" Please change this to marionette.log.level. We’re trying to deprecate marionette.logging. I’ve filed a follow-up bug https://bugzil.la/1434219 to take care of marionette.defaultPrefs.port.

Pushed by gbrown@mozilla.com: https://hg.mozilla.org/integration/mozilla-inbound/rev/8ec724e0a29d Enable marionette trace log for reftests; r=whimboo