Download a new copy of the Firefox installer from http://www.mozilla.com/ Delete the Firefox installation directory, default location is C:\Program Files\Mozilla Firefox\ For 64-bit Windows it is normally at C:\Program Files (x86)\Mozilla Firefox\ Re-install Firefox.

Deleting the installation directory will not delete your bookmarks, passwords and other user data, which are stored elsewhere.

I did what was written above, but it did not work

You did delete the "C:\Program Files\Mozilla Firefox\" directory?

It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.

See also http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall You can skip the step to create a new profile, that is not necessary for this issue.

After trying, failing, and reading again I found out that the solution is to install firefox in a directory with a new name.