I was able to get firefox to uninstall, then install by doing the following:

Delete the following folder: C:\Program Files\Mozilla Firefox

Open the registry by clicking start, type regedit in the search field, and hit enter. Navigate to HKey_Local_Machine\Software\ and delete the following three keys: Mozilla, mozilla.org, MozillaPlugins.

If you are running a 64-bit version of windows, navigate to the following key instead: HKEY_LOCAL_MACHINE\Software\WOW6432Node\

Then, Open up programs and features (or add/remove programs in windows xp), and click mozilla firefox and then click uninstall. You should get an error about not being able to uninstall and if you would like to remove the program from the list. Click yes.

Now you should be able to install firefox.

I would get rid of Funwebproducts. It is malware. I saw it in your user-agent.