User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.83 Safari/537.36

Steps to reproduce:

Firefox will render ordered lists with the wrong numbering, if you try to embed another ordered or unordered list as a direct child:

• Create an ordered list with a few elements.
• Embed an ordered or unordered list as a direct child of the ordered list between list items (see attached example).
• Observe the resulting numbering in the browser.

Actual results:

Firefox will trip and break the continuous numbering of the list entries within the parent ordered list. Both Chrome and Edge continue properly.

• The ordered list item following a direct child list will be off by 1.
• If the ordered list item follows an empty child list, numbering will be reset to 1.

Expected results:

Numbering of the ordered list should only be affected by list items (<li>) that are direct children of the parent element. Numbering should be consistent between list items, no matter other content.

Forgot to add: Actual example found in the wild. The numbering issue starts at caption 3/4.

This is invalid markup but anyhow this is fixed already on trunk, see bug 1548753 for the details.