Iceweasel or ABC has sand in the gears?

While youtube clips show (watchable, but not entirely smooth) motion in iceweasel on my new debian 7.8.0 install, ABC clips bearing the simple two-circle Venn diagram symbol in the TLH corner show only a static video image, and even the audio feed is interrupted. Is there some way to diagnose where the pipe is most constricted? (The 10 MB file at http://mirror.internode.on.net/pub/test/ took 20 seconds.) Does anyone else have trouble with the ABC's new video clip dingus? Erik