Sync wouldn't have done that. And Firefox doesn't "download" JSON files, which are used internally in Firefox which normally expose the user to their presence on the device.

What is the full name of those JSON files? Might give us an idea about how that is happening.

I tried attaching a picture showing the desktop and the JSON files downloaded, but I guess that photo was too big. A smaller picture is attached now. Here is the list of the files and folders on the desktop:

• add ons.json

blocklist.xml bookmarkbackups (folder) cache2 cert8.db compatibility.ini content-prefs.sqlite cookies.sqlite crashes (folder) datareporting (folder) directoryLinks.json extensions (folder) extensions.ini extensions.json features (folder) formshitory.sqlite frequencyCap.json gmp (folder) gmp-gmpopenh264 (folder) gmp-widevinecdm (folder) key3.db localstore.rdf logins.json mimeTypes.rdf minidumps (folder) permissions.sqlite places.sqlite places.sqlite-shm places.sqlite-wal pluginreg.dat prefs.js revocations.txt safebrowsing (folder) saved-telemetry-pings (folder) search.json.mozlz4 secmod.db sessionCheckpoints.json session-storebacksups (folder) sessionstore.js SiteSecurityServiceState.txt startupCache (folder) storage (folder) thumbnails (folder) times.json webapps (folder) webappsstore.sqlite xulstore.json

I uninstalled and reinstalled Firefox on my mom's desktop several times, but all of these files continue to pop on on the desktop when I click on the Firefox icon.

That looks like the entire Profile folder sitting on the desktop. Uninstalling Firefox and reinstalling it won't fix that. Somebody must have messed with the profiles.ini file or created a new Profile and specified the 'desktop' for its location.

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles#w_starting-the-profile-manager Launch the Profile Manager and then select a Profile that isn't highlighted.

Don't delete the Profile that is on the desktop, as that will delete everything on the desktop.

Those or some of them are parts of a Firefox profile. If Firefox is being Refreshed it will create such or simllar files but would be expected toput them in a folder and not directly on a Desktop. Its decades since I used a Mac so I find it hard to offer meaningfull advice.

I would suggest doing a clean reinstall of Firefox on the Macbook Pro. See

• Firefox keeps crashing at startup_try-a-clean-install
  • How to download and install Firefox on Mac

I think I solved the problem. It was definitely a Firefox profile issue. I deleted the 3 default profiles found, and created one in my mom's name. Somehow, before this fixed the profile manager in the Applications folder was missing. Now, Firefox is normal again.

Thank you for your help.