I had this problem that loading Facebook was becoming a problem because every time the home feed needed to load more stories the browser became unresponsive.

The moment I got close to the bottom the Javascript code to execute the fetch/render caused my browser to freeze.

This didn't happen on fresh Firefox sessions or Chrome, and the only extension that I have that affects javascript is Noscript! which should not be making javascript any slower!

Remembering the solution for the window.open error it came to me that the problem could be the stale surrogate functions my aged settings had.

What I did was export my Noscript settings, reset the extension's settings and export those again. On the file with the reset settings, I appended my old Whitelist and loaded this new file.

Now Facebook does not freeze as I scroll down, performance is not buttery smooth yet, but definitely a vast improvement. This shows that the problem was that the old surrogates were the ones affecting performance.

Lesson learned, check the release notes for new surrogates and update that manually since the new extension version will not change your settings.