I personally don't like Firefox HWA method. It has the 3rd best acceleration in the markes, but even with that, when I enable HWA, even settings the GPU (GTX560 Ti) to run in P0, I feel the browser is running a bit slower than in software mode, on a Intel Quad core from 4 years ago.
Opera 12.50 = the best acceleration, period. The freakin' whole thing is accelerated. (it's not final, though it's still the best)
Internet Explorer 10 = HWA is Microsoft's leading feature since IE9. So yeah, it's pretty good.
Firefox 10-15? = They kept adding more features to HWA, but they still have a long way to go.
Chrome = It accelerates only a few things, some times. You may activate all HWA-related flags and the browser STILL doesn't accelerate everything.