I was having an issue with Comcast and their downloaded set up system for my Windows 7 PC. Whenever I opened Mozilla Firefox, a series of Comcast tabs opened as a default. The most effective fix I have found will be listed step by step here.
Step 1: You must manually uninstall the Comcast setup from your Windows 7 Pc. I recommend running a search in the start menu. It will show all files and folders associated with Comcast. Select them all using the organize tab and delete them.
Step 2: Wipe your registry. I recommend using C Cleaner for this. The program is handy anyway for several different applications, as well as keeping your computer running smoothly. You can download it at http://www.piriform.com/ccleaner This will clear out any residual components.
Step 3 Uninstall Firefox. Yes uninstall it, and then reinstall it. This will wipe your user data and reset the browser.
If you find other methods that work feel free to post. I saw a posting for MaC users but nothing for PC. My Mozilla is now running smoothly but if there are issues with this method please inform me, So I can post a fix.