Preamble: yes, I've checked everything, dependencies, etc. and it looks like the noscript is the only thing that's causing the problem here.
I do use FF dev ed & FF stable, the problem surfaces in both versions.
I tested noscript stable & latest release. No difference.
The thing is, when I enable noscript, youtube icons (controls, to be specific) just disappear.
It looks like this:

(image from the Net, as I'm on other PC and had a while to write that here, but you get the idea)
Tried on clean profile, and just after I install noscript, icons/controls go to hell. Tried the same on my primary profile. Same result.
Clean noscript just after install causes that but I also tried resetting the one from my primary profile. Of course no difference.
If I want to disable noscript, I get the dialogue to either soft disable or hard disable it. Choosing the soft disable changes nothing. Only the "disable all protection" (and thus, disabling the extension completely) makes the embedded player work again as it should.
Any ideas?