Crashes or other problems with certain multimedia content in Firefox (such as Flash videos, animations or games) can often be resolved by performing the steps in these Knowledge Base articles:

• Flash Plugin - Keep it up to date and troubleshoot problems

• Adobe Flash plugin has crashed - Prevent it from happening again

Please tell us if this helped!

Flash is up to date.

What media player is used if you check this via the right-click context menu of the player area?

Is that the HTML5 media player?

A Flash based player shows a Flash context menu.

HTML 5.

The Cisco OpenH264 plugin is currently only used with WebRTC and not for playing videos.

http://andreasgal.com/2014/10/14/openh264-now-in-firefox/ You can try to disable hardware acceleration in Firefox.

Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available" You need to close and restart Firefox after toggling this setting.

https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration If it works in Safe Mode and in normal mode with all extensions (Firefox/Tools > Add-ons > Extensions) disabled then try to find which extension is causing it by enabling one extension at a time until the problem reappears.

Close and restart Firefox after each change via "Firefox > Exit" (Windows: Firefox/File > Exit; Mac: Firefox > Quit Firefox; Linux: Firefox/File > Quit)

In Firefox Safe mode these changes are effective:

all extensions are disabled (about:addons) default theme is used (no persona) userChrome.css and userContent.css are ignored (chrome folder in profile folder) default toolbar layout is used JavaScript JIT compilers are disabled hardware acceleration is disabled (Options > Advanced > General) plugins are not affected preferences are not affected