If you develop websites on either Windows or the Mac and use a virtual Windows OS program (like parallels), you might want to take a peek at IETester from DebugBar. The free tool is an all in one web browser that renders and uses the JavaScript engines for versions of IE8, IE7 IE 6 and IE5.5 on Windows 7, Vista and XP.
Learn more at My-DebugBar.com.

Good stuff – I use this a lot, but the only downside for me is that the IE7 browser view constantly crashes. If only there was something as simple for FF, without messing about with profiles and that allowed you to see multiple versions at once.
I have resorted to using Adobe Browser Lab: https://browserlab.adobe.com/index.html
I know there are others like it out there, but this does for me.
In addition, the Lunascape 6 browser allows you test different browsers.
Great tool. Glad you decided to come back!