Well, first the Version of Firefox you are running is extremely old and out of date. Let's try the following to get your Firefox back up and working:

Scan for Malware

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 some of the following programs to scan for malware:

• MalwareBytes' Anti-Malware
• TDSSKiller - AntiRootkit Utility
• Microsoft Security Essentials (A good permanent anti-virus if you don't already have one)

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

Update

After Scanning for malware, you have several things that are very out of date and are leaving you very vulnerable to viruses.

First, update Firefox to Firefox 15.0.1 Update Firefox to the latest version.

Then update your plugins. http://www.mozilla.org/plugincheck/

Finally, update Windows. windowsupdate.microsoft.com

Reset Firefox Finally, if this still doesn't work, try to Reset Firefox. Reset Firefox – easily fix most problems