Tried everything, made sure firefox pop-up blocker was disabled, re-installed firefox and flash designed for firefox re-installed umpteen number of times.

Tried going to the same site to play the same trailer at someone elses house who uses firefox, downloaded the firefox flash plug-in, disabled firefoxes pop up blocker, re-booted, same problem, its like flash was never on there in the first place when I went back to the page again.

I don't think firefox is capable of playing any trailer in flash!

Try it for yourself, open google using firefox, tap in WMC and goto the web site of wales millenium centre (top result). Goto WMC home page and click on CarMan or any other show/play they are offering details on, which has a trailer available to play when you click on it for more details. (trailer link usually top right of page detailing the show info).

See if you can play the trailers !???????

I'm now on Opera, the flash works no problem on opera, even using the very same download which was supposed to work on firefox, except now on opera I can't play yahoo games cos the Java doesn't seem to work on there! (Where it does with firefox) You just can't win!!
I think it's a fault with their site as my flash works fine on weebls-stuff, newgrounds and the other animator sites.
their website wont let you see their tralers with your firefox flash as well?
yeah, and I even tried the latest flash.

They have a site fault I'd say.
oh, thanks for trying, strange how those trailers on that site works fine with opera and IE though?!!
It's probably the developer didn't cater properly for firefox.
you know my flash vids were skipping and the audio was dropping in/out until I upgraded to version 9.045 [released 4/12/2007] of flash player. Now seamonkey works with flash.. yay..