Firefox fails to uninstall global extensions on Windows Vista due to the stricter user privilege. No problem on Windows XP. Current handling in my understanding: 1. set a flag needs-uninstall 2. delete the extension folder in the application directory when Firefox is restarted. Solution? 1. set a flag needs-disable 2. set a flag needs-hide The extension will only be disabled/hidden and still work with other profile, but I think it's a practical solution.