i preety much do what rexton85 does...
except that i don't like overloading ff with extensions.. it's allready a memory hog anyway..
So i wrote a bookmarklet for VideoDownloader. add to your bookmarks the section below.. Every time you visit a Youtube, googlevideo page etc, just click on that bookmark and a popup will come up with details on downloading your video.
Code:
javascript:var txt = "http://videodownloader.net/get/?url=" + escape(window.content.document.location.href) + %22&orig=ffp&ver=1%22;void(window.open(txt,'VD','fullscreen=no,toolbar=no,status=no,menubar=no,scrollbars=yes,resizable=yes,directories=no,location=no,width=800,height=400'));
Bookmarks