Created attachment 8631360 [details]
I'm guessing it tries to pull the credentials from my Firefox profile but perhaps it's using the wrong one? I'm currently using FirefoxDevelopEdition.
I've seen this error as well. I specify the bugzilla userid and cookie in my .hgrc. I'm able to publish from reviewboard and modify bugs in bugzilla without logging in again, so I don't think it's expired credentials.
It might be picking up the wrong Firefox profile. By default, it looks at all profiles in most recently used order and finds the first one with Bugzilla cookies. To bypass cookie lookup, default your Bugzilla username and password in your hgrc file. See https://mozilla-version-control-tools.readthedocs.org/en/latest/mozreview/install.html#bugzilla-credentials.
These problems should all go away once we switch to Bugzilla API tokens, which don't expire like cookies do.
This is actually probably bug 1184079, the fix for which was deployed last week.
*** This bug has been marked as a duplicate of bug 1184079 ***