We sometimes see a testrun fail under Mozmill 2.0 with the following message: > "A Firefox instance is already running...". I only managed to reproduce this once (around restart tests, under Ubunutu 12.04). Andreea has seen this failure several times (also on Ubuntu 12.04). I wasn't able to reproduce this under Ubuntu 13.04, OSX or Windows. Which seems to indicate that we might not able to fully close Firefox before trying to open it again. If anyone sees this again, please gather more info about it: - under which tests it failed - any weird failures on the tests right before (see if we had an unrecovarable crash)

This bug was most likely fixed by bug 966234.