So both Firefox 17 and Chrome 23 interpret a two-fingered right-swipe on my RMBP trackpad as a "back" gesture. This would be a really nifty feature if right-swipe didn't have the system-wide canonical meaning "drag the scrollable content right." You say, "What? No horizontal scroll gestures in Firefox and Chrome?!!" No, it's worse than that. You get horizontal scrolling until you can't scroll anymore, at which point your next swipe unloads the current page. Hope it was just a page, not a client-side webapp, or you just lost your work. Somebody fix this.
Edit: apparently this behavior is due to a misguided attempt on Firefox and Chrome's part to be good OS X citizens and implement the OS-wide "Swipe between pages" gesture, configurable in the "More Gestures" tab of the Trackpad Preference pane. Such a gesture may make sense for, say, the Preview app, but is a truly bad idea for a "page" that may contain dynamic content.