This is an extremely late answer, but two additional possibilities exist:
emacs-firefox-remote and jss. Neither has unfortunately been maintained in a rather long time.
The former does seem to at least have the ability to connect to firefox, retrieve some sort of information, and disconnect, though not very much else.
The latter is designed to be more extensive, providing support for debugging chromium as well. (However, I have not tested it, as in its case the code seems to be far too extensive to casually inspect, to ensure that it doesn't do something crazy.)
I hope that this is of some value to somebody.