STR:

1. Select "Strict" Content Blocking in about:preferences#privacy
2. Visit https://www.politico.com/magazine/story/2019/04/08/alexandria-ocasio-cortez-new-york-226578
3. Click the "Comment" button in the left sidebar to scroll down to the "SHOW COMMENTS" button at the bottom of the article.
4. Click the "SHOW COMMENTS" button.

Expected result:
Facebook comments should load.

Actual result:
Nothing happens when you click the "SHOW COMMENTS" button. Facebook comments do not load.

If you switch to "Standard" Content Blocking in about:preferences#privacy and reload the Politico.com page, then the Facebook comments will load as expected.

Affected version:
63.0a1 (2018-08-21) (64-bit) (build id: 20180821100053)

This basically means FB comments are broken with tracking protection which is a known issue. Linking this bug to two of the other examples.

While testing this I discovered that there is in fact cookie restrictions related breakage, just not what is described in Comment 0. I filed Bug 1545273 for that.

The technique in bug is helping here, but they load Facebook's SDK indirectly by loading https://s7.addthis.com/js/300/addthis_widget.js. As such, I have to whitelist that before the shim even kicks in, but then it works. One further complication is that they hide the comments by default behind a "show comments" button, so the user will have to click that, and then any placeholder we provide, before we would show the comments.

So this really seems to be a case where we need to handle AddThis, not just the FB comments.

The issue is still reproducible with ETP - Strict.
https://prnt.sc/xthj4g

Tested with:
Browser / Version: Firefox Nightly 87.0a1 (2021-01-29)
Operating System: Windows 10 Pro

If embedded Facebook contents require cookies from twitter.com (third party cookie) to embed contents, this is the right behavior.