If that’s the case, right-click the Policies key and select New>Key. It is possible that you may not have the Mozilla key under the Policies key. HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Mozilla\Firefox.Firefox Mac Os X 10.6 8 Mac users interested in Mozilla for os x 10.6.8 generally download: Firefox 81.0 Free Firefox is one of the most popular web browsers on the market, providing numerous helpful features and quick speed to millions of users worldwide.You need an extension for that such as Ad Block Plus inside Firefox (or any other browser for that matter. Firefox in itself is not an adblocker on a mac.Backup out one directory and open the userChrome.css file (create it if it doesn't exist) and add this line at the beginning of the file.