Open Firefox 5 or Firefox 6 (whichever version is installed on your system) and download a Firefox add-on named Add-on Compatibility Reporter.
Install the add-on and restart Firefox.
Download Google Toolbar and install it. Restart Firefox again.
NOTE: Google won’t allow you to download and install Google Toolbar directly from their website. To download Google Toolbar on your Firefox 5 and Firefox 6 follow the link given above.
After installation you would be able to use Google Toolbar on Firefox 5 and Firefox 6.
After our rigorous tests, we didn’t find any issue using Google Toolbar on Firefox 6. Firefox will keep sending the incompatible add-on message but it will not affect the usage anyhow. For any other Firefox tips or tricks, leave your comments.