User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:72.0) Gecko/20100101 Firefox/72.0

Steps to reproduce:

I visited support.mozilla.org

For example, this page: https://support.mozilla.org/en-US/kb/accessibility-features-firefox-make-firefox-and-we

I paged down, and it flashed.

Actual results:

support.mozilla.org uses a sticky black header, which often flashes if users page down.

This can trigger my migraines, and I doubt I'm the only one. I tend to avoid the site due to this and due to the search issues.

Expected results:

Even a position:fixed header would be an improvement over a flashing position:sticky header.

Looks like the header is not position:sticky now.

Position:sticky flickers should have been fixed by bug 1730998.