User Agent: Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:84.0) Gecko/20100101 Firefox/84.0

Steps to reproduce:

Nested list composed on an HTML email message has bad numbering caused by bad markup. This list was generated using Thunderbird UI and keyboard shourtcuts for nesting and unnesting elements (Tab and Shift+Tab)

<ol>
<li>11111</li>
<li>22222</li>
<li>33333</li>
<ol>
<li>11</li>
<li>22</li>
<li>33</li>
<li>44</li>
<li>55</li>
</ol>
<li>44444</li>
</ol>

Actual results:

The last item should be numbered as 4 but it is numbered as 6

Expected results:

Thunderbird should first generate better markup, so the nested list is inside a <li> element.

The rendering of list with wrong markup was already fixed on Firefox rapid release channel, the ESR bug #1684989 was closed. There is an option to backport it but maybe generating correct markup is a better solution