Recent releases of Firefox now work once again with Gnash. <a href="http://www.gnu.org/software/gnash/">http://www.gnu.org/software/gnash/</a> If you want a flash plugin for firefox 3 that: (1) is FOSS, (2) works with most sites, including Youtube, and (3) works natively in 64-bit versions, then Gnash is perhaps the FOSS alternative to Adobe that may suit you.