Rash of security exploits hitting Flash Player
If you have been wondering why Firefox is displaying errors on pages when you view a page with Flash content, it is because so many exploits have surfaced that Mozilla Corp has taken the extraordinary action of just blocking ALL flash even if the most recent version is installed. This isn't a problem we can fix and we aren't even sure we would want to 'fix' it if they are correct that several more 'zero day' exploits are coming soon.
You can override the block and allow Flash to display but you should only do so on a per site basis and only for sites you trust. YouTube, Vine and the really big Facebook games are probably safe but most other sites and EVERY ad server should be considered suspect until this mess blows over.
Stay safe out there....