Try to disable the hardware acceleration in the Flash Player. See Flash videos won't play full screen http://www.youtube.com/swf_test.html (right-click the player: Settings) Flash "Display settings" window: http://www.macromedia.com/support/documentation/en/flashplayer/help/help01.html

Seeing a green stripe on a media player usually means that the player overlay isn't fully covering the (green) space that Firefox reserve. You can try to set this pref to false on the <b>about:config</b> page. *media.wmf.dxva.d3d11.enable = false You can open the <b>about:config</b> page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue. *https://support.mozilla.org/en-US/kb/about-config-editor-firefox ---- You can try to disable hardware acceleration in Firefox. *Options/Preferences -> General: Performance<br>remove checkmark: [ ] "Use recommended performance settings"<br>remove checkmark: [ ] "Use hardware acceleration when available" *https://support.mozilla.org/en-US/kb/performance-settings Close and restart Firefox after modifying the setting for changes to take effect. *https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems You can check if there is an update for your graphics display driver and check for hardware acceleration related issues. *https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration