Flash hasn't been working for a few months in Firefox on my machine. I finally got sick of have in to switch to IE every time I used iPlayer or YouTube so decided to investigate. It appears that the is a bug with the current version which incorrectly tries to impose the 64bit plugin on 32bit browsers like Firefox. So I have downgraded the version to 11.2.202.235 which included a 32bit installer. This can be downloaded from the archive page on the Adobe website (http://helpx.adobe.com/flash-player/...-versions.html). I wouldn't normally recommend downgrading, but it seems this is the only way of getting it working.