i would hazard a guess that you have the real player downloader installed in firefox, if you disable it in add ons /extensions then play flash videos will work.
my workaround to keep both working was to roll back the flash player update and re enabling the real payer downloader.
until realplayer update the downloader for the latest flash palyer, (they used to)
edit. just noticed you are able to watch vids now, the roll back works.
let me know if you have realplayer downloader installed,out of interest.