Running two versions of Firefox under Mac OS X couldn’t be simpler. The freeware application MultiFirefox takes all the guesswork out of the process by automatically detecting Firefox versions in your main Applications folder and presenting you with a list from which to choose the Firefox versions you’d like to launch. Complete with self-updating (thanks to the ubiquitous Sparkle framework), MultiFirefox is the easiest way to pull off this multi-browser stunt. Now to Windows Users Download Firefox 2 and Firefox 3 , depending on what you already have installed. Launch each installer and begin setting up Firefox, but make sure to choose Custom settings. When asked for a place to install Firefox, change the path(s) to C:\Program Files\ Mozilla Firefox 3\ (or …\Mozilla Firefox 2 ) , instead of just “Mozilla Firefox” . In doing so, you’ll place Firefox 2 at C:\Program Files\Mozilla Firefox 2\ , and Firefox 3 at C:\Program Files\Mozilla Firefox 3\ . Both versions of Firefox should n...