According to Mozilla Links, Firefox 3.1 will be getting the rumored update to tab switching that got a little buzz after Firefox 3 was launched. 

As said, there’s also a new behavior for Ctrl + Tab. Instead of just moving left to the next opened tab, now it switches between the current and the last viewed tab and I have to say I’m already loving it. I usually have to check several other pages while posting and to ease the tab switching I moved the reference tab next to the post edit tab to have it a couple of keystrokes away. There’s no need now: I just took the long way to the reference tab once and then it’s already at reach.

Want this feature now?  Check out the Ctrl-Tab add-on for Firefox.