Do a clean (re)install and delete the Firefox program folder (C:\Program Files\Mozilla Firefox\).

Download a fresh Firefox copy and save the file to the desktop.

• Firefox 13.0.x: http://www.mozilla.org/en-US/firefox/all.html

Uninstall your current Firefox version, if possible.

• Do NOT remove personal data when you uninstall your current Firefox version, because all profile folders will be removed and you will also lose your personal data like bookmarks and passwords from profiles of other Firefox versions.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.
• http://kb.mozillazine.org/Uninstalling_Firefox

Your bookmarks and other profile data are stored elsewhere in the Firefox Profile Folder and won't be affected by a reinstall, but make sure that you do not select to remove personal data if you uninstall Firefox.

• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Profile_backup

• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall

Are you using a third-party browser, like Waterfox? As the Waterfox download page says, you need to have Visual C++ 2010 Redistributable Package (x64) installed to use it. See http://waterfoxproject.org/downloads/

Also note: There is a support link on the Waterfox website. It points to http://www.overclock.net/showthread.php?t=975626. For any further help with Waterfox, it's best to use their forum.