When BC Preservation is pref'd on, we get multiple firefox UI test failures. See:

https://treeherder.mozilla.org/#/jobs?repo=try&author=kmachulis%40mozilla.com&selectedJob=245636424

https://treeherder.mozilla.org/#/jobs?repo=try&author=kmachulis%40mozilla.com&selectedJob=245636630

These need to be fixed before turning the pref on permanently.

(In reply to Kyle Machulis [:qdot] [:kmachulis] (INACTIVE) from comment #0)

These need to be fixed before turning the pref on permanently.

We did pref this on later, so presumably these failures were no longer happening at that time.

I also see that there were later Try pushes by qdot where the failures were no longer occurring (the push linked in comment 0 was from the 9th May):

https://treeherder.mozilla.org/#/jobs?repo=try&author=kmachulis%40mozilla.com&selectedJob=245636424

No longer failing on a later push of the 14th May:
https://treeherder.mozilla.org/#/jobs?repo=try&author=kmachulis%40mozilla.com&selectedJob=246278641

https://treeherder.mozilla.org/#/jobs?repo=try&author=kmachulis%40mozilla.com&selectedJob=245636630

No longer failing on a later push of the 14th May:
https://treeherder.mozilla.org/#/jobs?repo=try&author=kmachulis%40mozilla.com&selectedJob=246278734

So this bug looks like WORKSFORME, unless I'm missing something.

Per comment #1, it seems the failures were no longer occurring, so close as WORKSFORME.
(we could reopen or file a new bug if the failure happens again)