For me they have nothing (success! :)
I use Firefox + FB container + uBlock Origin + Privacy Badger and recently started to use CanvasBlocker as well. I have Firefox configured to delete all cookies on closing (except for few sites to avoid the need to enter the 2FA code every time I log in).
I've also set Firefox Enhanced Tracking Protection to "Custom mode" with "cross-site and social media trackers" blocked [1] and to use block list "level 2".
I also have the "Do Not Track" option switched on.
I don't have a proper smartphone (never owned one), just KaiOS-powered dumb-phone on which I use Facebook mobile (i.e. their web site) all the time.
Also no Pi-Hole or similar stuff.
I use a throwaway email account for Facebook.
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[1] Just now I've found out that there seems to be a new option, to disable "all cookies from unvisited sites", which I'm going to try as it looks even better.