In my previous entry, I described how one could set up selenium to runs tests from emacs, via the Moz REPL. The most painful part of all of that is setting up the REPL to run. After every firefox startup, you have to manually go to tools menu, and manually select 'MozLab' and then 'Start REPL'. YUCK.

It would be nice if you could somehow automatically run javascript on Firefox startup.

Enter UserChrome.js. With a little more polish, some documentation, and something more then a MozillaZine forum posting for a website; this little extension is poised to become the new GreaseMonkey. It will be the GreaseMonkey for the hard core.

Once you have installed the extension, you can now run Javascript on the creation of every new Mozilla window (even sub windows like prefs, downloads, etc.) or just the main window. From this point, it is almost painless to start the REPL:

// Anonymous function application to 
(function(){
	var repl = Components.classes["@hyperstruct.net/mozlab/mozrepl;1"].getService(Components.interfaces.nsIMozRepl);
	if (repl && (!repl.isActive()))
	{
		repl.start(4242);
	}
})();