"Mozilla has shipped Firefox 3.5.6 with patches for at least 11
documented security vulnerabilities."
It is recommended that you update your Firefox to the latest version to
fix these issues.
It should be noted, updating to 3.5.6 on my machine broke my Profile.
It could be related to an add-on that I have and may not affect you or
your users. To fix, I created a new profile from scratch.