This looks like a useful service, but just wanted to point out that having a JS embedded button might not be the best way of going about it, or at least in it's current form with the historious_key as the only means of authentication. If a site is expecting historious users, it can have a simple javascript polling loop that wait until the historious bookmark is activated to jack the key.
Also, there is a Chrome extension available and we will be writing more as time progresses (sadly there are more important issues to address).
Thank you very much!