This intermittent was likely occurring because we set the expiry timeout
for temporary permissions to a really low value in the previous test.
The failing test was only failing on slow machines, leading me to believe
that the time between setting and checking was larger than the 500ms timeout
defined in the previous test. Thus, the permission was reset on checking it.
The expiry pref was set using pushPrefEnv, which restores prefs only after
the entire test was run. To just eradicate this category of problems in
the future I moved the test that manipulates the expiry into its own file.
MozReview-Commit-ID: 3mc5xHY4XLn
