You have a number of extensions, including AdBlock and TorButton, that could be blocking full screen mode.

Follow the steps at Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems to see if an extension is keeping you from using Flash in full screen.

I have tried in safe mode and as expected it makes no difference. I am still not able to view in full screen like IE it just shows a blank white screen. I was able to view full screen with the same extensions before so removing them has not made any difference.

Thank you for your reply anyway.

I have reloaded Flash Player 10.0 and I can now watch BBC iPlayer in full screen. Thus, IE shows iPlayer in full screen with Flash Player 10.1 on my computer and Firefox does not.

Thanks anyway.

Cheers.