First, Firefox profiles are created using a random string of numbers. So, 'g4xfs73z.default' would be a normal name. '''Transfer User Profile Files''' https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles ''When you are ready, we can start moving parts of your'' ''old data and '''Copy''' it to the new profile.'' ------------------ First; open your file browser to the '''New''' profile; Type '''about:support'''<enter> in the address bar. Under the page logo on the left side, you will see '''Application Basics. ''' Under this find '''Profile Folder. ''' To its right press the button '''Show Folder. ''' This will open your file browser to the current Firefox profile. Now '''Close Firefox. ''' '''Linux: ''' Under the page logo on the left side, you will see '''Application Basics.''' Under this find '''Profile Directory. ''' To its right press the button '''Open Directory. ''' -------------------- Second, open another file browser to the '''Old''' profile. Open another file browser to the Old Firefox folder on your desktop. Then open the folder with the latest date. '''Warning ! ! ''' Only '''Copy''' the files you are told. We will avoid anything that might cause problems. Here is the list of files; '''cookies: ''' cookies.sqlite Do not bother. Cookies will be created when you return to the website. However, you will have to log in everywhere. And you may lose any settings that websites store on your computer. '''extensions(add-ons, themes): ''' it would be better to download them fresh. ++++++++++++++++++++++++++++++++ '''key3.db''' [v58+] '''key4.db''' and '''logins.json''' : These are the password files. '''Copy Both ! ''' '''persdict.dat''' : custom dictionary – words you added to the dictionary '''mimeTypes.rdf''' [v55+] '''handlers.json''' : What to do with what type of file. '''places.sqlite''' : History and Bookmarks. '''prefs.js''' : Your settings. '''Note:''' If you were having problems, this could be contaminated. '''cert8.db''' [v58+]'''cert9.db''' and possibly '''cert_override.txt''' : Stores all your security certificate settings and any SSL certificates you have imported into Firefox. If removed, the '''cert8.db''', '''cert9.db''' file will be replaced. '''search.json.mozlz4''' : file stores the user-installed search engines that are available in the Firefox v47+ '''search.sqlite file''' and '''searchplugins folder''' store the search engines that are available in the Firefox Search bar '''before''' Firefox v47 +++++++++++++++++++++++++++++++++++++++++++++++++ '''Copy''' these files from the old to the new. You may get a message that the files already exist. Choose to '''over-write''' for each file.