Yeah, no, not worth it at this point and the Win XP machines software are set up as close as possible but with respect to hardware they are all different. About six laptops and maybe ten desktops (plus some Linux desktops). The good thing is that if and when one machine fails or has a problem I can just go to another machine which is set up pretty much the same. But, as I say, it is strange that these quirks come up where one machine behaves differently.
In this case I was pretty sure it was some Firefox configuration setting but nobody could tell me where to look.
Anyway, it is good that it is working now and I can see videos again.