Browserplugins are really useless and crappy - I would never ever download something like that as a customer. First, I have to download the game itself, no matter what - then I could just download the binaries - and second, I would have to install another plugin into my browser, slowing it down.
No use, a lot of work, so well, useless. If youre serious about creating in-browser-solutions, rather go with Java or Flash.