Lion full-screen (http://bugzil.la/639705) is coming in Firefox 14, which will be released six weeks from today (https://wiki.mozilla.org/RapidRelease/Calendar). You can use it now on the Aurora channel (https://mozilla.org/firefox/aurora/) and in a few days it'll also be on the Beta channel (https://mozilla.org/firefox/beta/).

Lion-style scrollbars (http://bugzil.la/636564) are still in progress. You can test them on the UX branch: https://msujaws.wordpress.com/2012/03/15/mozillas-ux-nightly...