The trick to backups is testing them
. At a minimum you should create data backups of pics, music, software keys, etc.
Good to hear MalwareBytes came up clean. Do you have CCleaner? It's a simple program that cleans up the junk files on your computer. You can get it at your favorite download site or directly from them. I recommend the "slim" version that comes without the optionally installed toolbar.
The slim build is at the bottom of this page.
http://www.ccleaner.com/download/builds
Note: CCleaner will clean up your browsers cache, cookies, history, etc. It also allows you to check or uncheck items that you do or do not want cleaned. I would run the cleaner regularly to keep things tidy. Don't mess with the registry cleaner and if you do, make a backup when it asks you to before fixing the issues.
I wish I could help more. The 3.5 version of Firefox should be out soon (July?) as it's already a release candidate. I know some folks have had memory issue with Firefox while others get along fine. With 3 tabs open I'm at 91,000K but my system is no slouch.