'''More detail please...''' What OS? What version of Firefox? I'll guess Windows... If windows, home or pro? If windows, are you running any security software besides MS Defender? If Windows Pro version, try testing in Windows Sandbox (VM) to see if you have the same issue. https://www.howtogeek.com/399290/how-to-use-windows-10s-new-sandbox-to-safely-test-apps/ This video may be helpful. How to Fix the ‘PR_END_OF_FILE_ERROR’ Secure Connection Error https://www.youtube.com/watch?v=-_gyBDZiFDw