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.

Some sites use HTML5 Video others use a Mixture of both.

https://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html Then install Flash Player Version: 27.0.0.183 https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) Note: Other software is offered in the download. <Windows Only>

Do this please : https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration TRY NO HARDWARE ACCELERATION Then : https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems?redirectlocale=en-US&redirectslug=Troubleshooting+extensions+and+themes

Note it shows here your running version 56.0 but have no idea what your running with send info turned off. Current version of Firefox is 56.0.2 https://www.mozilla.org/firefox/all/ Full Version Installer

Note : Firefox 57 Quantum release date Nov 14th https://www.mozilla.org/en-US/firefox/quantum/ Note : Legacy Extensions will be disabled and or removed.

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

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block (wanted) content (e.g. Adblock Plus, NoScript, Ghostery, uBlock Origin) always make sure such extensions do not block (wanted) content.

• make sure your extensions and filters are updated to the latest version

You can find a Lego block icon at the left end of the location bar indicating that the web page uses a plugin (Flash) that Firefox might block. You can click this Lego block icon to allow or block this plugin.

• https://support.mozilla.org/en-US/kb/why-do-i-have-click-activate-plugins