Allow height and width to be given to allow responsive testing

[jamescookie]

Both PhantomJS and Chrome allow you to give the initial dimensions of the browser to allow responsive testing, but not firefox.

I thought it would be trivial but it turns out not to be simple.

Modifying this line to the following should work, but doesn't?

self._execCommand(command, [url, '-profile', self._tempDir, '-no-remote -width 335 -height 670']);

This is what I did get working, but it's not pretty - Add the following before this line:

fs.writeFileSync(self._tempDir + '/xulstore.json', '{"chrome://browser/content/browser.xul":{"main-window":{"width":"335","height":"670"}}}');

Obviously, the height and width should be passed in (I was just tinkering to try to get it to work)

Maybe something else altogether?