Comment 15 for bug 518422

Bug 530196 is probably a symptom of this issue.

Another symptom may occur on linux builds where extensions containing components are symlinked. For example, on Debian, extensions can live in a common directory for all applications and /usr/lib/mozilla/extensions/{app-id}/{ext-id} is a symbolic link to the common directory.

Another trigger was reported by a user who uses symbolic links for his firefox profile.

What happens then is that while you can run firefox once, if you exit firefox and start it again, well, it doesn't start up.

It looks like the xptiInterfaceInfoManager part of bug 491245 is responsible for this issue. In other words, reverting its hunk (http://hg.mozilla.org/mozilla-central/diff/51bafb458d68/xpcom/reflect/xptinfo/src/xptiInterfaceInfoManager.cpp) is enough to "fix" the problem.