Yesterday Firefox 4.0 was released and web developers everywhere celebrated a really great browser.  The browser comes packed with a super fast JavaScript engine called JägerMonkey. Now don't get too excited just yet! We still need to keep that old version of Firefox around for testing; we can't assume everyone has upgraded to Firefox 4. So, to run both Firefox 3.6 and Firefox 4.0 on the same machine, just follow these simple steps:

• Open up your Applications folder and find your old version of Firefox

• Right click-> get info.

• Rename to "Firefox36.app"

• Download Firefox 4.0 and install as normal

• Celebrate that you now have 1 more browser to test in!

Really simple! If someone knows how to do this on the Windows and Linux side, I would love to hear how.