Sorry for the late reply.
If anything I think the Norton extension might be part of the issue.
Outside of that I’m not super clear on what would be causing this. We’ve ruled out quite a few things and it seems to be mostly limited to Facebook. I’m going to have to reach out to a couple colleagues about what else we can try/test here.
In the meantime, if you wanted to run another test, you could download the Brave beta build and test to see if Facebook exhibits the same behavior there. Note that downloading/installing the Beta will not overwrite anything related to your current install. It will just install as a totally separate browser can be uninstalled once testing is done.