It seems like you did all the things in the right way, but there must be a problem in resetting firefox itself. We suggest you to reboot your computer and then try it again. If this also doesn’t work then boot your computer in “Safe mode” and then try the same method once again. If this trick doesn’t work, then try method 2.
Method 1:
Follow the following steps
Open Firefox >> Option >> Help >> Troubleshooting Information
Click on “Refresh” Button. See the following screenshots for reference.
If the above usual method did not work for you, then you have to reset firefox browser manually, try method 2.
Method 2:
Close the Firefox browser and then remove the Firefox profile folder (example: 2xwk4pl1.default) from “C:\Users\{user-profile}\AppData\Roaming\Mozilla\Firefox\Profiles\” location.