Just follow the following steps and you will be able to login in gmail and orkut with multiple accounts. Through this you will be able to make profiles in your firefox.
Open system properties(by right clicking my computer), choose tab advanced, click to environment variables button. in system variables section, click new. type this information to each textbox.
variable name: moz_no_remote (should be all small letter).
variable value: 1
open firefox icon's properties(from desktop and quick launch). add extension -p to command line(like "c:\program files\mozilla firefox\firefox.exe" -p). press ok.
When you will open firefox it will prompt for profile selection create a profile,open firefox login to orkut open once more use another profile login.