Selectively port mixedpuppy's changes to the selenium command line to no longer require moving of /Applications/Firefox.app

This ports the changes so that we don't need to move the Firefox.app on Mac, basically by specifying the Firefox binary to use.

It also ports Shane's changes which provide logging of behind-the-scenes items, e.g. firefox.log so that we can see what is happening if we need to.

Suggest review from @fqueze