Question marked as
Third party installed fonts can be the culprit ..
Open the Font Boot app located in HD > Applications.
From the Font Book menu bar, click Font Book > Preferences then click Resolve duplicates by moving files to the Trash.
Quit and relaunch Safari to test on Facebook.
If the problem persists, with the Font Book app open, back to the menu bar, click File > Restore Standard Fonts > Proceed. That restores to the standard system font configuration and will remove any nonstandard fonts from the system font database. Fonts not included in the MacOS system install will be placed in a "Fonts Removed" folder next the Fonts folderQuit and relaunch Safari to test again.
If that didn't help, a Safe Mode boot deletes system caches that might work for you.
To start up in safe mode:
- Start or restart your Mac, then immediately press and hold the Shift key. The Apple logo appears on your display. If you don't see the Apple logo, learn what to do.
- Release the Shift key when you see the login window. If your startup disk is encrypted with FileVault, you might be asked to log in twice: once to unlock the startup disk, and again to log in to the Finder.
To leave safe mode, restart your Mac without pressing any keys during startup.