I have recently setup a development 2008 R2 Remote Desktop Host Server to test Firefox ESR 10.0.3. I can set the options to not check for updates and that works correctly. However a standard user seems to be able to go to Help>about and the application auto updates. I am slightly concerned about this being an Enterprise server. Is something setup incorrectly to not have any UAC trigger with this and disallow an update of the application?
Firefox installs a service that can do updates even if the program was installed to the %programfiles% directory, and the currently logged in user has no admin rights and no right to modify files inside %programfiles%.
You can uninstall that updater service, the rest will still work fine.
Also you can lock preferences to certain values, for all users. For example you could use this to completely disable the builtin updater. Then users cannot switch it back on. A good description about this is here: http://mike.kaply.com/2012/03/16/customizing-firefox-autoconfig-files/