FirefoxADM is an open-source project dedicated to the goal of being able to manage large numbers of Firefox installations on a network using the Windows Active Directory Group Policy Objects (GPOs).

Using FirefoxADM or ADMXPI, you can

• Lock settings such as homepage, proxy and many others in Firefox
• Set defaults on many settings within Firefox
• Create a profile on user first usage
• And feature list ever growing (already on way to same feature-completeness as IE's Group Policy setting features)

All of these settings can be set via Group Policy as it is possible for Internet Explorer.

This project originally started of as a bunch of VB-scripts to be used as logon/logoff scripts (the original FirefoxADM), but was soon changed to be implemented as a Firefox XPI extension. This version was rebranded as ADMXPI for Firefox and currently is the recommended version to use.
There is also a version of ADMXPI for Thunderbird, which allows system administrators to set Thunderbird presets via Active Directory GPOs.