They are working on it on several fronts, constantly cutting off tasks from the main thread onto their own ones (downloading, cache v2, Awesomebar), making other things asynchronous (project snappy), garbage collection improvements also help in some cases. Most of these are smaller wins, and several big ones like OMTC, tiled rendering or e10s are yet to come.

Edit: It may not be as responsive as Chrome (I don't know as I don't use it), but I believe it is miles ahead of it's former self.