skipping the firefox version validation if firefox is not the browser be...

...ing used


@jzoldak @benpatterson 

This makes it so that a user doesn't have to use `--skip_firefox_version_validation` to get around the firefox version error if they are not even using firefox.  As in, if I'm running tests in chrome, I shouldn't get an error saying `Exception: Required firefox version not found.`

RE @benpatterson 's comment:  This still allows someone that is using firefox to say "don't validate the version". It just makes it so that it will not check the firefox version when someone is using a non-firefox browser.