I get a black screen when starting Firefox. Safe Mode works. I went through the process of uninstalling and reinstalling Firefox and fixing and resetting and opening in safe mode and disabling add-ons and unchecking hardware accelerating as described in the troubleshooting advice. I am at the point in troubleshooting where I am supposed to change to the default theme but I find it disabled. There is no checkbox to enable the default theme. How do I enable the default theme? If enabling the default theme is there anything else I can to get past the black screen when starting Firefox?