Facebook thinks LibreWolf, a hardened privacy oriented Firefox, is no longer supported.
When I went into Facebook to check for updates from my family, I got this little popup in the bottom left corner saying, "Your browser is no longer supported. Please update to a newer version for the best experience.", making me wonder if its actually Meta stupidity or shittery since LibreWolf is up to date.
One of the simplest forms of anti-fingerprinting measures is falsifying the User-Agent HTTP header. Librewolf probably does this, thus Facebook thinks you have an unsupported browser.