Rename to Firefox::Profile to allow for Firefox.pm, potentially

The Ruby and Python bindings are able to run tests without a Remote
Webdriver session being open on localhost:4444. I'd guess they're
searching for the Firefox binary and then injecting a profile with the
Webdriver extension, and if we're ever interested in implementing
similar Remote driver independent functionality, I'd imagine it could
go in Selenium::Remote::Driver::Firefox.