After installation of  Windows Update KB976002 you will get after a restart a browserchoice selection where you can choose for Firefox, Safari, Internet Explorer etc etc.

I would understand if you don’t want this to be on your workstations of your domainusers.

With this GPO setting (rightclick and Save As…) you can change the registry at your clients. The GPO file contains the following:

CLASS Machine

       CATEGORY “Custom Policies”

       CATEGORY “Internet Browser Selection”
 
       POLICY “Enable Browser Selection”
 
   EXPLAIN “As set Enabled, the user will have the possibility to choose browser”
   KEYNAME “Software\BrowserChoice”
   VALUENAME “Enable”
   VALUEON NUMERIC 1
   VALUEOFF NUMERIC 0

  END POLICY

 END CATEGORY

END CATEGORY