Firefox plugins

FF portable is setup so it doesn't load plugins from harddisk. And in the portable drive folder for plugins are these: flashplayer.xpt, nppdf32.dll(10.1.4.38), NPSWF32.dll(11.5.500.85), NPSWF64.dll(11.5.500.85)

And it work on most web videos, fx this one works: http://www.youtube.com/watch?v=LRBc1t06paw&feature=relmfu

But then there are often also some that just appear as a black box, fx. this one: http://www.youtube.com/watch?v=ri8rju7sZLI

And it doesn't even report "Missing plugin", it's just black. But if same URL is opened with IE installed on harddisk it does work.
And it's impossible to find plugins on harddisk. It's a public PC, perhaps they are hidden.

So what's missing on portable to play it?