Now that Mozilla officially supports Customizing Firefox Using Group Policy on Windows, this project has been archived.
Be sure to check out the policy templates and the latest releases.
To install the Firefox ADMX templates, copy the contents of the ADMX folder into \\ad.domain.example.com\SYSVOL\ad.domain.example.com\Policies\Policy Definitions
In order for the polices you set to apply, you need to add the firefox_start.vbs script to the Computer Configuration > Windows Settings > Scripts > Startup section of the GPO you are applying to an OU.