Without knowing what the reasons are, that the Uninstaller does not work, I can advise you:

In most cases a clean installation of firefox is not necessary, simply download the setup-file from the official Mozilla Firefox Download-Site, and install it. The Installer will take care of the rest for you.

tl;dr: You don't need to uninstall via Control Panel.

Regards,

The System Details list next to the question shows a Firefox 7.0.1 version, but since you posted with an IE (?) user agent we can't check this via the user agent.

See:

• http://kb.mozillazine.org/Uninstalling_Firefox
• https://support.mozilla.org/kb/Uninstalling+Firefox

If you can't uninstall Firefox then delete the Firefox program folder.

• (32 bit Windows) "C:\Program Files\Mozilla Firefox\"

You can find the full version of the current Firefox release (51.0.1) in all languages and all operating systems here:

• https://www.mozilla.org/en-US/firefox/all/
• https://www.mozilla.org/en-US/firefox/notes/