I'd love to see something for firefox. I don't know if you could do something like a href=mailto but instead, make it bitcoin and put the address there like a hyperlink. The addon would then open up bitcoin with the address. I don't know if I want to send directly from the browser, but to at least copy over addresses for me would be nice. Even a little box with my bitcoin total would be fun and a dialog or alert without interference that a payment has been received.
The thing that gets scary about doing things automatically from a browser is when malicious people decide that they can take your whole wallet with a bad site.
I already thought about this problem. I came up with this idea:
Have bitcoin (or some proxy program (I was thinking about this for my pybitcoind-desklet program) in between) start a dbus daemon that accepts "bills". These "bills" list the receiver address, the amount of bitcoins, the program sending the "bill" and possibly a transaction description. On receiving the receipt, the user gets a pop-up/notification about the "bill" to pay it and the user is free to accept or decline the bill. After that the money is send or not.
Via this, possibly every program has a standard interface to connect to for sending bitcoins and there is no direct connection to the rpc interface, so malicious programs can't do any harm (e.g. sending rpc commands that it isn't allowed to do.
