I used a Firefox add-on for this a few months ago, but I don't think it was ever updated for compatibility with the webextensions API. If I'm remembering correctly, it was this: https://addons.mozilla.org/en-US/firefox/addon/fb-purity-cle...

Worked very well for me. No reason you can't spin up an older version of FF (or 52 ESR) just to use this add-on.

I cleaned out all of my account's information first, and then slowly weaned myself off of use of the News Feed when I had free time. Eventually I wasn't even logging in once a week and just up and deleted my account.