We're running SA's on 7.0R4 and 7.1R1.0. Several users that upgraded their Firefox from 3.6 to 4 complain they are unable to have software like the Setup software and HostChecker pushed to their clients. When they downgrade to 3.6 it is working again. So my advice: wait a while before upgrading your Firefox 3.x users to 4.
It has something to do with user customization. I just uninstalled Firefox 4.0, and deleted all of the mozilla entries from the registry under HKLM\Software\ and HKCU\Software. I then installed firefox 4.0 using the typical option. After logging into 7.1R1.1, I was able to open an RDP session to a windows machine.
I then uninstalled Firefox 4.0, cleaned the registry, and installed firefox 3.6.16 using the typical option.
I then verified that rdp connectivity worked.
I then installed firefox 4.0, without uninstalling/cleaning.
I then verified that rdp connectivity works.
My initial installation, overtop of 3.6.16 w/ noscript/adblock/ie plugins didn't work, and I'm going to try to re-create that failure scenario.
(edit 1: deleted dup word)
After removing 4.0 and re-installing and reconfiguring 3.6.16, rdp worked. after upgrading to 4.0, I was unable to re-create the problem.