Incidentally the sound is fine just no picture;lots of intersting noises but nil to see
that used to always be associated with codecs, and the sort of standard workaround was to install VLC player, as that can play pretty much every format out there, that said, it will also (on its default install settings) associate itself with all of those file types during install, and a shit load of your icons for files will switch to traffic cones
but as we're talking browser based, then yeah it could be flash related, or perhaps silverlight (if that's still used)