Adblock: I tried Adblock for Chrome and it had problems, so I switched to AdThwart which uses the Adblock Plus blocklist but it doesn't seem to work as well as ABP for Firefox. I also have a hard time adding my own rules to the filter. I'd say it's worked only once or twice out of all the times I tried it.
Mouse Gestures: This is probably kind of picky, but my favorite and probably most often-used feature of All-in-One Gestures for Firefox is that when I do an upward gesture it will open a new tab, but if I do an upward gesture on a link, it will open that link in a new tab. I haven't been able to find another gesture extension that does that.