I've yet to find a good Firefox cleaner that does it all... The best one I know of seems to have its link gone dead.
Best I can do is give ye these step by step manual instructions:
1. Make sure you can view hidden/system files and folders.
2. Go to Control Panel>Add/Remove Programs in Windows XP; or Control Panel>Programs & Features in Windows Vista, and if a 'Mozilla Firefox' entry (or similar) exists, select it and click Change/Remove and uninstall it. During uninstallation, tick the 'Remove my Firefox personal data and customizations' box as well - note that this will delete all of your bookmarks and saved settings, so make sure you've backed up your bookmarks and also note down any passwords which you might otherwise forget.
3. Find and remove all Firefox/Mozilla-related entries in the Windows Registry. Using the Windows Registry Editor (Start>Run>Regedit), delete any of the following keys if they exist - that is, right click on their name in the left pane of Registry Editor and select Delete:
[HKEY_CLASSES_ROOT\FirefoxHTML]
[HKEY_CLASSES_ROOT\FirefoxURL\]
[HKEY_CURRENT_USER\Software\Classes\Applications\firefox.exe]
[HKEY_CURRENT_USER\Software\Mozilla]
[HKEY_CURRENT_USER\Software\MozillaPlugins]
[HKEY_LOCAL_MACHINE\SOFTWARE\Mozilla]
[HKEY_LOCAL_MACHINE\SOFTWARE\mozilla.org]
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxHTML]
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\FirefoxURL]
4. Rename (or delete) the Firefox folder in the default profile path (or move it to a backup location). For example, on Windows XP, click the "Start" button, select "Run", type in %APPDATA% and click "OK" to open the hidden "Application Data" folder, then open the "Mozilla" folder and rename the "Firefox" folder.
Caution: Make sure that you rename the entire Firefox profile folder, which includes the profiles.ini file that keeps track of profiles. Do not simply rename or delete the profile folder that contains your user data, as doing so can result in a "profile in use" or "already running" message when you next attempt to run Firefox (bug 278860).
Note: If you also have Mozilla Thunderbird or any other Mozilla products installed, make sure to only delete entries under the keys above which specifically relate directly to Firefox by name.
Also delete:
C:\WINDOWS\Prefetch\FIREFOX* files
(XP)
C:\Documents and Settings\<username>\Application Data\Mozilla\Firefox\
C:\Documents and Settings\<username>\Local Settings\Application Data\Mozilla\Firefox
(Additionally, in Vista):
C:\Users\<username>\AppData\Roaming\Mozilla\Firefox\
C:\Users\<username>\AppData\Local\Mozilla\Firefox
C:\Users\<username>\AppData\Local\VirtualStore\Program Files\Mozilla Firefox
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"Security Vulnerabilities Count-Up -Internet Explorer: 158, Firefox: 209." - FirefoxMyths.com
Thothie