A Firefox update or re-install should not change the profile folders. However, there have been cases of this happening.

Look on your desktop. Do you see a folder called; Old Firefox?

https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

Type about:profiles<enter> in the address bar. How many profiles are listed? How many should be there?

Yes I see a folder call Old Firefox Data.... how should I proceed?

I just copied my Firefox profile to a different location, updated the app, and then copied the old profile back but still a complete history wipe once updated.

djdunks said

Yes I see a folder call Old Firefox Data.... how should I proceed?

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.

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 and logins.json : These are the Password files. Copy Both !

persdict.dat : custom dictionary – words you added to the dictionary

mimeTypes.rdf : 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 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 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.

Just to be clear, It says the "Old Firefox Data" folder has not been modified since Nov 2016 so Im curious how that could be storing recent browsing history?

You would only restore what is in the files you are working from.