Looks like there's a bug in the latest version of Firefox that's causing it to block various add-ons, such as Adobe Flash Player. Mine was OK up to about an hour ago, now I'm told I have an outdated version of Flash installed. Nope! Here's what I'm seeing instead of a youtube vid:
Strange thing is, if I click on the 'Check for Updates...' button I get taken to a Mozilla web page that tells me I have the latest version (I know that!)
Clicking on 'Activate Adobe Flash' and then on 'Activate Now' seems to be the temporary solution.
Problem has been reported on the Mozilla support forum:
https://support.mozilla.org/en-US/questions/1035859