Try this

• https://support.mozilla.org/en-US/kb/firefox-wont-start-find-solutions

Open TaskManager, if it running firefox.exe > end all processes

Sometimes a problem with Firefox may be a result of malware installed on your computer, that you may not be aware of.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• TDSSKiller - AntiRootkit Utility
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Did this fix your problems? Please report back to us!

Thank you iamjayakumars. I have performed a complete system restore. The problem I described is after the restore. After trying to start firefox, task manager does not show firefox running. After starting firefox and waiting a very long time to see what happens, a script error occured. After a couple of times trying the wait game, a type of script error was shown. I found this link on support, seems to be what is happening, but as you see that fix did not help either.

https://support.mozilla.org/en-US/questions/980011?esab=a&as=s&r=0&page=2

Here is the answer that took care of the problem,

http://kb.mozillazine.org/Browser_will_not_start_up#Problematic_plugin_prevents_browser_from_starting

"TrueSuite Website Log On" (AuthenTec) plugin, is the issue.