This vid contains tips that help fix Class not registered while trying to view some local/network file, or open some app you installed.
Solution 1: Run System File Checker sfc /scannow (note the space between sfc and "/") If SFC did not find any violations it is still a good idea to run DISM Restorehealth Dism /Online /Cleanup-Image /CheckHealth If you have trouble completing the cmd codes above, perform a clean boot in Windows. If the issue persists, create a new user account. See more@ support.microsoft.com/en-us/help/17197/windows-10-set-up-accounts Then, move your personal files to the new account and/or other disks on your computer.
Try reinstalling/repairing your Firefox -> if that does not work, completely remove it using the recommended uninstall tool in this video guide > restart > perform a clean install of Firefox. And, delete any newly added theme-type files. 4. Cube Browser?