''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. ''' Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder '''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. -------------- '''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. If you need to remember what add-ons you had, open the '''extensions''' sub-folder and look at the '''.xpi''' files ++++++++++++++++++++++++++++++++ '''logins.json''' and '''key3.db''' [v58+]'''key4.db''' : 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.

For the passwords you need logins.json and key4.db. For the bookmarks you can copy places.sqlite (bookmarks and history) and also possibly copy the bookmarkbackups folder with the automatically created compressed .jsonlz4 JSON backups. See also: *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile