I had to downgrade Firefox. Before I did I created a new profile so we would not lose the old bookmarks. Now Firefox downgraded and no bookmarks or profile. Then I upgraded back to the latest Firefox and still no profile or old bookmarks. Can anyone suggest where they might be?
Note: With some versions of Firefox, the data files are not backward compatible. If there is an issue, create a new profile and we can tell you how to recover the data.
Step one: How do you completely turn off update checks in Firefox v64? You can use a policies.json file to disable updates for all users. https://github.com/mozilla/policy-templates/blob/master/README.md or https://winaero.com/blog/disable-updates-firefox-63-above/
You can use a policies.json file in the distribution folder in the Firefox installation folder instead as also listed in the article, so no need to use GPO keys in the Windows Registry. • https://support.mozilla.org/en-US/kb/customizing-firefox-using-policiesjson ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ You can use the ManualAppUpdateOnly policy in Firefox 87+ to enable only manual updates e.g. via "Help -> About Firefox".
Note that it is important to stay up to date and install the latest security patches.
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 box.
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/Open 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. You should see it on the directory "tree" in the first file browser. Right-click on that folder and select Open In New Window.
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.