I'm pretty sure it has vdpau support:
Originally Posted by stmiller
I'm able to see smooth full HD flash video (with medium to low CPU usage), using method described here. I have a flash update pending though (10.4). I will update this info if the new plugin has some issues.
$ strings /usr/lib/firefox/plugins/flashplugin-alternative.so | grep -i vdpau
H264 - VDPAU - CPU
H264 - VDPAU - VDPAU
@stmiller, could you test that in your system?
EDIT: I updated to the latest. The 'strings' changed a little bit, but the plug-in still supports acceleration.