Please consider turning on send info to Mozilla before posting a question. This helps us help you. As I have no info from your system that would help see things that cause issues.

I really have no idea how to help with out some information like the state of your video card drivers,, Extension list, am I looking at the correct version of Firefox installed 56.0

Firefox handles both HTML5 and Flash Video with no issues...unless there is a issue. Update your video card drivers as that is where the issue usually begins. https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration TRY NO HARDWARE ACCELERATION

How about you uninstall and then reinstall Firefox 56.9.2 which is the current version from a Full Version Installer https://www.mozilla.org/firefox/all/

See how it goes after you have done those 2 things. If come back list your extensions,

Please let us know if this solved your issue or if need further assistance.

sorry, how do I send info to Mozilla? I didn't see an option when posting my message. my video driver is up to date and when changing the settings for "Hardware Acceleration" it seemed to work so I didn't go any further with your suggestions.

thank you

attached is my extensions

What do you get in the player area when this problem occurs?

Do you notice the plugin notification icon on the left end of the address bar at that time? That is where you could grant the site permission to use Flash. You won't always get the gray panel in the player area if the site is showing a "poster" image instead.

You can look at uBlock Origin as a replacement for Adblock Plus to see if that works better.

• https://addons.mozilla.org/firefox/addon/ublock-origin/

thanks for you advice, I am making notes of all of them in case I have trouble in the future.

jscher2000, seeing that it hasn't happen since I took Pkshadow advice I really don't know.....

thank you all!!