How to Unistall Firefox
If you have a previous version of Firefox before Version 2.0, I strongly suggest that you uninstall it and then install the full 2.0 package or newer. This will prevent a wide range of problems down the track. Once Firefox 2.0 is installed, you can then use the automatic update feature to keep it up to date quickly and easily. Uninstalling Firefox doesn't remove your bookmarks or settings/tweaks by default. However uninstalling and cleaning out all the Firefox files including your profile(s) is also an excellent way of resolving any extremely strange behavior or annoying problems you may get with Firefox. In any case, if you want to completely remove all traces of Firefox from your system follow these steps:
1. Go to Control Panel>Add/Remove Programs in XP or Control Panel>Programs & Features in Vista, and if a 'Mozilla Firefox' entry (or similar) exists, select it and click Change/Remove and uninstall it. Reboot if required.
2. Go to your Documents and Settings\[username]\Application Data\Mozilla directory in XP, or the \Users\[username]\AppData\Local\Mozilla and \Users\[username]\AppData\Roaming\Mozilla\ directories in Vista and delete the entire \Firefox subdirectory and all of its contents. Note that this will delete all of your bookmarks and saved settings, so if you want to backup any or all of your current Profile, see the Customizing Firefox section on page 7 of this guide first. Typically all that I would recommend you backup and restore is your bookmarks.html file.
3. Go to your \Program Files\Mozilla Firefox\ directory and delete it and all of its contents.
4. Using a registry cleaner like RegCleaner 4.3, find and remove all Firefox/Mozilla-related entries (usually there are several Mozilla entries to be found) and remove them. Alternatively you can use the Registry Editor (Start>Run>Regedit) and delete the following keys - that is, right click on their name in the left pane of Registry Editor and select Delete:
That will remove the bulk of the Firefox-related settings which can cause problems with newer installations if they have become corrupted (through overclocking for example). Note: If you also have Mozilla Thunderbird or any other Mozilla products installed, make sure to only uninstall entries under the keys above which relate directly to Firefox.
In most cases you should only have to undertake Step 1 of the above list. However again I must stress that if you are having any problems with Firefox and nothing else in this guide works to resolve it, then I suggest you follow all the steps above. Once again if you need to backup any of your bookmarks or settings first, read the Customizing Firefox section before following the steps above; fully uninstalling Firefox as detailed in steps 1 - 4 above deletes all your customizations, settings and history.