Not Diablo 3 but cool news nonetheless. According to Kotaku.com a programmer named GalaXyHaXz has been working on a Diablo fan project called Devilution which "ensures everything is preserved as it was originally designed". This includes bugs, bad code, and more. This project made it possible for a modding group called Rivsoft to make the game playable via browser. You can do so at DIABLO
If you own the original Diablo you can drag and drop the DIABDAT.MPQ file from the installation folder to begin playing that version in the browser instead of the modded.