Completely by accident, I discovered that you can now drag a tab out from its current window to a new window in a recent Firefox nightly. A short video 24-second better explains what I'm talking about:

This tab tearing capability is a pretty neat feature - I know you can already do this in Safari, Opera and Galeon. It's really well done in Safari, which I think is what Firefox is emulating. Nice to see Firefox follow suit!

If you can't wait for Firefox 3.1, try it out in a recent Firefox nighty build (remember to use a new profile unless you are willing to risk corrupting your daily profile).