Try:

• http://kb.mozillazine.org/Corrupt_localstore.rdf

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.org/kb/Safe+Mode

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

This could possibly be caused by

• corrupt (or multiple) prefs files
• or interfering software extensions (some of the plugins and add-ons that you use with Firefox)

1. First of all try using firefox in safe mode <-- click link for instructions --
   • there is no need to make changes in the first Window with an options list just click on continue (amongst other things safe mode temporarily disables all your add-ons)
2. If problems continue then whilst still in safe mode disable all plugins.
3. Finally try re-setting your preferences. This will make some changes
   • see How to fix preferences that won't save (The easiest resetting method is to use the safe mode options, that I initially suggested you should avoid ! )

Note that particularly after an upgrade some security etc software may fail to recognise firefox components or, attempt to reset/restote them, what security related software is in use?

Problem solved. Following the above advice I went into safe mode, disabled all the add ons and then re-enabled each to see which one was causing the problem. Turns out the offending add on was the all-in-one sidebar add on. Finally I removed the add on then downloaded and re-installed it again. Now everything is working as it should. Thanks for the help.

Glad we helped and that you solved the problem. Thanks for posting back with the solution.

(I marked your own post as the solution)