Either way, this is a great way to prevent brute force attacks from determining a user's password, as well as preventing a serious incident should a website store credentials in plain text, then get compromised.

Of course, in a perfect world, everyone should be using unique, random passwords for each account they have on the Internet... but this is a great way to protect people that are using relatively insecure passwords across the board.

I'd suggest allowing custom salts so that users can enter their bookmarklet on other browsers, enter their "custom salt," and be able to get additional randomness. If this were to catch on, we wouldn't want people adding the salt to cracking tools etc (although that would be a lot more work/processing power on their part).

Sorry this was long winded. Cool idea, nice implementation!