Comment 3 for bug 1640255

Pushed an addition to both branches to support allowing the browser to ask the extension if it's available. It uses sendMessage() to send a 'ping' request and get an immediate 'pong' response (or lack thereof) to determine if the connection is installed in the browser.

The previous code simply opened a port, which may never respond, which was an unreliable way to determine if the extension is available.

Note that I was having some trouble with the old web staff statusbar code when testing Hatch. Before testing, I recommend also merging the branch from bug #1564508.