How to delete key3.db in https://kb.mozillazine.org/Profile_folder_-_Firefox#Files ?? I don't know how to delete files pls answer...I want to delete master password...
It's now called the primary password. Try Settings > Privacy & Security > Logins and Passwords > unselect Use a Primary Password. I don't know whether that works and I don't want to try it. I doubt that deleting the file you mention will do what you want; I would leave it alone.
Note: The key3.db file is no longer used. The current files are logins.json and key4.db