You should probably try the newest Firefox 10.0.0.2, I think. FF 11 will be out soon.
You might lose some of your extensions/add-ons. Many add-on developers have stopped updating because of Mozilla’s Rapid Release insanity.
Check out the add-on ‘Is It Compatible?’ to see which of your current add-ons are compatible with the later FF editions.
https://addons.mozilla.org/en-US/firefox/addon/is-it-compatible/
==
You can delete FF cookies by going to the Tools >> Options >> Privacy and Security and Advanced/Network tabs
You can also run a 3rd party cleaner. CCleaner is a good, free-for-home-use one.
http://www.piriform.com/ccleaner
Thank you for the info