Sorry to hear about this problem. If you haven't already, please try a normal Windows 10 shut down and restart to release file locks and complete pending updates. If problems persist: Could you try starting Firefox in its Safe Mode? In its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, any userChrome.css/userContent.css files, and some other advanced features to help you assess whether these are causing the problem. Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.) A small dialog should appear. Click "Start in Safe Mode" (''not'' Refresh). Any improvement? ---- You also could try: '''Clean Reinstall''' This takes about 5 minutes. It's not about your settings, it's about making sure the program files are clean (no inconsistent or alien code files). As described below, this process does not disturb your existing settings. It's not essential to uninstall Firefox, but you can if you like, saying No to any request about removing personal data. (A) Download a fresh installer for Firefox to a convenient location: https://www.mozilla.org/firefox/all/ (B) Exit out of Firefox (if applicable). ''If you use '''Microsoft Office''', please change your default browser to Internet Explorer temporarily before the next step.'' (C) Using Windows Explorer/My Computer (hold down the Windows key and press E to launch it), right-click > rename the program folder as follows (you might have one or both): C:\Program Files (x86)\Mozilla Firefox =to=> C:\Program Files (x86)\OldFirefox C:\Program Files\Mozilla Firefox =to=> C:\Program Files\OldFirefox (D) Run the installer you downloaded in step (A). It should automatically connect to your existing settings. Any improvement at your next startup? ---- If neither of the above helps, there may be a problem in your profile, but that will need more diagnosis.