Firefox requires uac permission to start and only recognizes one user regardless of who is logged on.
Since auto-installed upgrade on 11/27, when firefox is started a UAC popup appears asking for administrative permission for firefox to modify computer. Program starts when permission is granted, but one user profile is the only one accessible to all users, regardless of who is logged on. System is Windows 7, 64 bit.
Opaite Mbohovái (1)
Check that you do not run Firefox as Administrator.
Right-click the Firefox desktop shortcut and choose "Properties".
In the Compatibility tab, make sure that Privilege Level: "Run this program as Administrator" is not selected.
You also need to check the Properties of the firefox.exe program in the Firefox program directory.