firefox hanging problem on upgrade of firefox Rated 5 out of 5 stars
To the two most recent reviewers, and others who may have this problem:
upon upgrade of firefox from 3.5.6 to 3.5.7, it appears that this addon prevents firefox from closing normally.
the solution is to disable, then reenable this addon, and then the problem gets fixed, as described in this ubuntuforums thread:
To the addon author: please try and figure out the source of the problem. it seems to be reproducible, since multiple people have it on multipre os's.