Could you please expand on this issue and tell us more as not fully understanding your issue. When does this happen ? What pages does this happen on ? Do you have a screen shot or can you supply one ? The more information you supply the better we can try to help solve your issue.

Let me start by saying that Flash and HTML5 are two different technologies.

Flash-formatted media plays in a plugin. Your Firefox reported that it has Flash 27, but individual sites may need permission to use it. Please see this article for more details: Why do I have to click to activate plugins?

Firefox's built-in HTML5 player can play other formats of media. Here's a general article as a starting point for problems with HTML5 players: Fix video and audio problems on Firefox for Windows N editions.