Deleting profiles on user appdata folder is not able to reset or refresh Firefox in a Windows OS, even a new re-installation will not help also.
So how to refresh Firefox like it was a first installation?
Well, it’s quite simple and straight forward resetting Firefox like resetting a device to its factor settings.
Open Firefox, click on “Help”. If “Help” menu does not appear on the menu bar, press “Alt” key on the keyboard so the menu bar will display.
Click on “Help”, then click on “Troubleshooting Information” then click on “Refresh Firefox”.
See screen shot below:
After clicking on “Refresh Firefox”, all settings, add-ons will be completely gone.
This process is very useful, if you experience nasty or unwanted toolbars, websites keeping popping up out of nowhere, if you do this process it will solve the issue.
But if for some reason by doing this process, unwanted websites are still opening as new tabs. Then it could be some other issues, you will need a malware or anti-virus to clean your system.
MalwareBytes, Avira and other free anti-virus is quite helpful. But if you want have some extra penny then a purchase anti-virus is much better because all functions of the software is available.
If you have some important bookmarks backup or export the bookmarks before doing this process.
Cheers..Hope it helps.. Have a safe browsing.