Let me address things one at a time.
Solving your firefox problem:
1. Keep a copy of your bookmarks folder to restore them later. Just copy this folder at someplace safe.
If you are on Windows 7/Vista, keep a backup of this folder - C:\Users\<username>\AppData\Roaming\ Mozilla
If on Windows XP, backup this folder - C:\Documents and Settings\<username>\Application Data\ Mozilla
2. Uninstall Firefox, when you are on it, firefox asks you if you want to keep the user data, make sure that you opt for deleting all user data present. (this deletes most of the Firefox trace from your computer)
3. Download and install the latest stable build of Firefox and import book marks from the Bookmarks menu in Firefox. Also install the Addons freshly, do not overwrite the Mozilla folder which you have backed up earlier.
Importing bookmarks makes sure that you only get the book marks back and no other old files/cookie. By reinstalling addons, you can make sure that which one was causing the problem, and a fresh install always works the best.
This should solve your Firefox sluggishness.
