Facebook embed blocks not previewable and cause console errors in customizer

[timph]

steps to replicate:

1. Create new post
2. Add a new Facebook Embed block (I used same URL from Theme Unit Test Data as this is where it was noticed: ​https://www.facebook.com/6427302910/posts/10156380423617911/ ).
3. Save and publish post.
4. Visit post on frontend of site - no console errors appear.
5. Click Customize in adminbar.

The result is that console errors reported, and the embed does not display giving inaccurate previews in the customizer:

5uPlmwCxNZ9.js:70 ErrorUtils caught an error: "Failed to set the 'domain' property on 'Document': Assignment is forbidden fo...". Subsequent errors won't be logged; see https://fburl.com/debugjs.

[matdemystify]

I'm getting the same issue and it's a block on us using gutenburg, i do wonder if it's not browser specific. weirdly changing to the default theme it worked more consistently.

[whyisjake]

Hey there @timph. It looks like Facebook and Instagram are going to be dropping support for unauthenticated oEmbed requests October 24th and as a result, we will be removing this feature from WordPress core. There are a few plugins that will be providing support if needed. See #50861 for more info.