This may be related to T108357: Line breaks pasted as <br>s in Firefox.
Steps to reproduce:
- Type a new list:
* Food ** Apples ** Blueberries ** Cherries
- Then press Return (get a new "** list item") and Return again (get a new paragraph). Type a new paragraph.
- Notice that the "new paragraph" is not properly aligned. The first character is aligned with the first character of the level-one list item, rather than on the left margin where it belongs.
- Save the page. Check the diff. The last item is ** List item new paragraph when it ought to be
** List item New paragraph
 Why didn't pressing Return again un-indent to a "* list item"?