Shumway is a more direct route to solving this problem than reverse engineering the Pepper API. The Shumway approach has several other advantages too, such as portability and unifying the graphics/audio/JIT stacks of the browser and Flash. Assuming Shumway works out (that's a big assumption, but so is assuming that Pepper could be reverse engineered and shipped), I don't see any technical obstacles to Firefox doing this as well.