So tried to set up for a dump, going the 2GB route, after using memlimit to limit visible ram to 2GB's, YouTube no longer hangs here. Videos do hang after a few seconds of playing and it didn't take long to run out of memory, obvious by the output and get the usual trap 3 trp.
'Tis weird, I guess I should run memcheck
David, could your also test lowering your memory, or did you when getting your dump?