Download latest Firefox version using one of these links:

• http://www.mozilla.com/en-US/firefox/new/
• http://www.mozilla.com/en-US/firefox/central/
• http://www.mozilla.com/en-US/firefox/fx/
• http://www.mozilla.com/en-US/firefox/all.html

Uninstall your current Firefox

• https://support.mozilla.com/en-US/kb/Uninstalling%20Firefox
• DO NOT SELECT TO REMOVE USER DATA AND SETTINGS
• Restart your system

Install Firefox using the downloaded & saved Firefox installer file

• https://support.mozilla.com/en-US/kb/Installing%20Firefox%20on%20Windows

Check and tell if its working.

Hello Ed,
Just run run the executable downloaded file in an admin account. (You may need to look at UAC or security software settings).

The standard install, will overwrite the existing installation files, but try to leave the user profile, and therefore bookmarks passwords and settings intact.

• see installing Firefox on Windows <-- clickable link ---

N.B.
Any particular reason why you are choosing to upgrade only to 3.6.22, the version may not be supported for much longer the standard release is Firefox 6, which updates in about a week to Firefox 7.

• see also updating firefox