Comment 26 for bug 226165

Just experienced same problem. "sudo firefox" solved the problem, but this is of course an unacceptable solution from a security point of view. Then I noticed that a couple of files in my firefox profile directory were owned by root for some reason. (Might this be the result of installing a new toolbar as root? (which I did...))

Thus, upon executing "sudo chown -R <my username>:<my username> " here my problem was solved :)
The profile directory can be found in ~/.mozilla/firefox/, the one with a really random name :P

hope this helps