Firefox 3.5 includes support for the multi-touch features of the latest and greatest MacBooks, but leaves out a "twist" motion that moves forward and back through browser tabs. A quick about:config hack brings it back.
Photo by jeffturner.
CrunchGear points out that the easiest way to get at and configure the "twist" motion, made by turning two fingers as if they had a rubber ball between them, is to launch into about:config from the address bar, confirm that you won't mess up anything, and type "twist" into the filter bar. The two items you want to double-click are browser.gesture.twist.left and its .right counterpart. Set them to Browser:NextTab and Browser:PrevTab, respectively, and you're on your way.
You may want to modify the timing of the twist motion's responsiveness, or do the same kind of modifications to other multi-touch gestures, so hit the link below for more suggestions and an original instructions link.