Can you provide me more info ? Does it happen only start up ?

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 You can check if there is an update for your graphics display driver and check for hardware acceleration related issues. *https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration