Firefox will not start or is it the update?

Some protection programs don't like the update/install stubs. Go here for the full installer.

http://www.mozilla.org/en-US/firefox/all/ Download Firefox For All Languages And Systems

After getting the update, Firefox prompts for a restart. Once I hit the restart button it shuts down. It does not restart on its own and clicking the icon on my computer does nothing. I cannot get it to work until after I have gone back to the pre-update version.

OK, Did you do what was suggested and get the full install at the URL showing ?

Can try this : https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode

Please follow this: https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware

If returning please give expanded point form details of the issue. List all your Extensions & Anti-virus/Firewall please. More information is needed to help you further after you have completed the above URL's recommended to you.

or Please let us know if this solved your issue or if need further assistance.

It isn't malware and I've tried the safe mode and the refresh firefox. Still not resolved. Looking at the taskmanager it looks like the previous firefox session is not fully closing. The window closes, but the process in the taskmanager doesn't and prevents a new session starting. This has only just started in the last couple of days.

Okay. It is definitely something in the update. If I disable updates and do not run the latest one then I can close and open firefox freely. Whatever it is in the update that handles the restart and relaunch is causing a problem. Other than just not updating firefox any more, I don't know what to do here.

Please file a bug report here. Provide Full details and answer any questions asked. Once your report is filed, please post the bug report web page here. Good luck.

https://bugzilla.mozilla.org/ See Bugzilla etiquette before commenting in bug reports. https://bugzilla.mozilla.org/page.cgi?id=etiquette.html