The os/2 build is not generating a registry.dat file along with the Users50 directory. Consequently, mozilla does not remember multiple profiles and always creates a default one at startup. Currently, in xpcom\io\nsDirectoryService.cpp, HOME_DIR for os/2 is set to NS_OS2_HOME_DIR, but there is no home directory concept on os/2.
Set HOME_DIR equal to NS_OS2_DIR. This will make mozilla create the Users50 dir and registry.dat in the OS2 system directory (i.e. c:\os2). See attached diff file above.
r=dougt. This patch is OS2 specific and will not hurt anything.
Fix checked in.