Yeah... Ok, I probably deserved a bit of a snarky reply -- I missed the 32-bit requirement for silverlight in the release notes (apparently their sandboxing for 64bit is broken). Just for that oversight, I'll take my lumps.
I do think, however, that you're thinking in a binary way about this. It's possible to add new features and fix bugs at the same time, ya know. It's possible to prioritize stuff even in a beta... you don't just pile on the shiny new because you slapped a "beta" sticker on it.
It's a beta release, not an alpha, and the eighth beta release. Right on the durn frontpage is says it should be stable enough for normal use in most cases. I would classify youtube as one of those cases.
As soon as the 7th release came out, it was broken in an obvious way vis a vis youtube video on some platforms. They had months to fix it. Mozilla obviously decided that WebGL bling was more important...
...and that's fine, they can do what they want and yes, it's a beta release and webgl is cool, but I still think their priorities are screwed up.