add start-ff-clean

add task to start firefox in a clean environment
fix error in main-cs module

this code needed to be touched, because jshint didn’t like the old way it
was written. Unfortunately the "fix" was wrong, of course the check and the
has to be _inside_ of the function. This prevented the plugin from working
in firefox and everything seems to work fine, again.
Merge pull request #164 from johnyb/firefox_enhancements

Firefox enhancement/fix