Start Firefox in <u>[[Safe Mode|Safe Mode]]</u> to check if one of the extensions ("3-bar" menu button/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem. *Switch to the DEFAULT theme: "3-bar" menu button/Tools > Add-ons > Appearance *Do NOT click the "Refresh Firefox" button on the Safe Mode start window *https://support.mozilla.org/kb/Safe+Mode *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes It is possible that security software (anti-virus, firewall) is causing the problem. Try to disable security software temporarily to see if that makes a difference. Boot the computer in Windows Safe mode with network support to see if that has effect in case security software is causing problems. *http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/ *http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10