fix Linux firefox command args so that it's now possible to start a new
Firefox browser instance at the start of the test, and close it at the
end of the test -- it still leaves the test runner around after the end
of the tests if there was already an active Firefox instance before the
tests were run.
Always create a new Firefox instance rather than attaching to any
pre-existing instance -- as a result I can now run the full build
whether or not I have an instance of Firefox started beforehand.
Merge pull request #178 from BladeRunnerJS/firefox-tests-working-on-linux

fix Linux firefox command args