Safari Version 11.1.2 (13605.3.8) breaks Facebook

Do you have the Dashlane extension installed?

Try setting up another admin user account to see if the same problem continues. Please post back on whether or not this worked. Also try the Safe Mode. Please post back on whether or not this worked.

Isolating an issue by using another user account

Safe Mode - About

Safe Mode Startup – El Capitan. also Sierra

If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor. Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown.

Etrecheck – System Information

Historiacally, browser extension developers are the group most like to be "behind the curve" in keeping up with Safari updates. Anytime Safari acts out after a update, suspect lazy extension deveopers.

There is some evidence developing that multiple ad blockers work at cross-purpose and slow Safari. Find ONE you like and don't add any more.

Do you have any safari extension installed?

Do the issue occurs in a private browsing window?

Safari/Safari Extensions - there are several to try.

My personal favorite is AdGuard, it uses the content blocking mechanism introduced in OS X El Capitan.