See if this happen in [https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Safe-mode] , if this is not happen then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears. Use "Disable all add-ons" on the Safe Mode start window to disable all extensions. [https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems?redirectlocale=en-US&redirectslug=Troubleshooting-extensions-themes Troubleshooting extensions and themes] thank you Please mark "Solved" the answer that really solve the problem, to help others with a similar problem.