Try creating a new profile exclusively for 4.0 and create a desktop shortcut with -P "profile" appended to the target to launch that profile.

• http://kb.mozillazine.org/Testing_pre-release_versions

• http://kb.mozillazine.org/Creating_a_new_Firefox_profile_on_Windows
• http://kb.mozillazine.org/Shortcut_to_a_specific_profile
• http://kb.mozillazine.org/Using_multiple_profiles_-_Firefox

Tried that and still get the same result when starting my computer about mozsqlite3.dll being missing so spoolsv won't start and saying that a re-install will fix it.

Have even done a clean install after totally removing firefox and still the same problem

Do you see that file in the Firefox program folder ("C:\Program Files\Mozilla Firefox\") ?

Do a clean (re-)install:

• Download a fresh Firefox copy and save the file to the desktop.
• Firefox 4.0: http://www.mozilla.com/en-US/firefox/all.html

• Uninstall your current Firefox version and remove the Firefox program folder before installing that copy of the Firefox installer.
• Don't remove personal data if you uninstall the current version.
• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.

Your bookmarks and other profile data are stored elsewhere (not in the Firefox program folder) and won't be affected by a reinstall, but make sure that you do not select to remove personal data if you uninstall Firefox.

I have done a clean re-install even removing all the personal data and still the problem persists.

The file is in C:\Program Files (x86)\Mozilla Firefox folder but isn't in there for version 3, only version 4.

Firefox 3.x versions don't use that file, it's new for 4.0.