In the past I tried to find a solution for FireFox, but always came up short. Well today I did a google search and came up with two different ones!
both are FireFox extensions
after a quik spin with both I am liking CookieSwap better
With CookiePie you right click on the individual tab to toggle seperate cookie sessions on or off; just didn't have good luck using it the way I would do stuff with IE
With CookieSwap you right click in the lower right hand status bar area of FireFox and can toggle between named profiles (default is Profile1, Profile2, Profile3) - this worked right out of the box as I would expect!