For users of Firefox 50, there is a bug when you try to see flash videos on some websites. Firefox compains that you need to upgrade libavcodec. You need to open the about:config, then you type in libavcodec. media.libavcodec.allow-obsolete;true : This is the way it should be. By default, now it is false. This is the simplest way to have flash playing in Firefox 50.
rowdy