Would not know : Please consider turning on send info to Mozilla before posting a question. This helps us help you. As I have no info from your system that would help see things that cause issues. Suggest : Updating your Graphics Card Drivers as old or corrupted drivers cause issues. As well viewing HTML5 Videos could make a difference in performance and quality. Because no info for your system it is hard to diagnose what could be the issue as you present several that are not typical to other people's issues have seen in recent versions. Repair System Registry and Files (FOR DOING Above & Below - WINDOWS All OTHER VERSIONS - Use Search To Find Command Prompt ** Enter CMD.exe to Find COMMAND PROMPT Then Right Click & RUN AS ADMIN) To run the SFC command use the Windows key + X keyboard shortcut to open the Power User menu and select Command Prompt (Admin). Type "SFC /SCANNOW" (without quotes or copy/paste) and press Enter. For more information on using SFC, please refer to the Microsoft KB: Use the System File Checker tool to repair missing or corrupted system files Run the Windows Deployment Image Servicing and Management (DISM) and System File Checker (SFC) tools as Administrator. The DISM and SFC tools scan the integrity of the Windows image and all protected system files replaces corrupted, damaged and incorrect versions. (FOR DOING Above & Below - WINDOWS All OTHER VERSIONS - Use Search To Find Command Prompt ** Enter CMD.exe to Find COMMAND PROMPT Then Right Click & RUN AS ADMIN) Type "DISM /Online /Cleanup-Image /RestoreHealth" (without quotes or copy/paste) and press Enter. Windows 10 To run the DISM command use the Windows key + X keyboard shortcut to open the Power User menu, then select Command Prompt (Admin). Type "DISM /Online /Cleanup-Image /RestoreHealth" (without quotes or copy/paste) and press Enter. While running DISM you may notice the process will appear to pause at 20%. After a few minutes the operation will continue. Note : SFC fixes files locally using files found on your system. Note : DISM goes up to Microsoft for new ones. Do know that Windows 10 can and will replace your Hardware Drivers with Microsoft's. You would need to explore in the Device Manager. https://www.howtogeek.com/302595/how-to-stop-windows-10-from-automatically-updating-hardware-drivers/ Suggest since it is not just 1 issue as mentioned you can follow this : Please uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Then restart system. Then run Windows Disk Cleanup. Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. Reinstall Current Release Firefox 56.0.2 with a Full Version Installer https://www.mozilla.org/firefox/all/ If still issues the problem maybe in your profile. The past year has been gearing up for this : https://www.theinquirer.net/inquirer/news/3020724/firefox-quantum-everything-you-need-to-know-ahead-of-next-weeks-release or you can wait a few days and Firefox 57 Quantum release date Nov 14th https://www.mozilla.org/en-US/firefox/quantum/ Note : Legacy Extensions will be disabled and or removed. Please let us know if this solved your issue or if need further assistance.