Add Firefox support to regexp

[Niek]

Firefox nightly supports CDP out of the box, although not everything is implemented (see https://wiki.mozilla.org/Remote). I'm experimenting with connecting to Firefox using this library, and this is a small change in the regexp that's required to connect to FF. For anyone interested in testing: I'm using spawnWithWebSocket and passing the Firefox executable with arguments ['--remote-debugging-port=0', '-url=about:blank'].