User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.121 Safari/537.36 Edg/85.0.564.63

Steps to reproduce:

First the environmental details:
Thunderbird Version: 68.12.0 (64-bit)
OS: macOS Catalina Version 10.15.7

Now the bug:
Thunderbird does NOT handle nested HTML lists well - the example below is an unordered list nested in an ordered list, but ordered lists within ordered lists are also a problem.
I EXPECT that nested lists would be displayed as they would if the list were pasted into https://www.w3schools.com/HTML/tryit.asp?filename=tryhtml_lists_intro
Reproduction details below:

1. Compose a new message
2. Click inside the compose message area
3. Choose Insert > HTML
4. Paste the following:
   <ol>
   <li>Coffee</li>
   <ul>
   <li>White</li>
   <li>Black</li>
   </ul>
   <li>Tea</li>
   <li>Milk</li>
   </ol>
5. Click insert
   ==========================
   The nested un-ordered list causes the numbering sequence of the ordered list to FAIL - item 3. Tea SHOULD BE item 2. Tea
   The good news is that if the recipient has a well behaved email client (e.g. gmail) then the recipient's email will display the list properly.
   The bad news is that if someone sends ME a properly formed list, TB does NOT display it properly.

Actual results:

1. Coffee
   ° White
   ° Black
2. Tea
3. Milk

Expected results:

1. Coffee
   ° White
   ° Black
2. Tea
3. Milk

(In reply to rednectar.chris@gmail.com from comment #0)

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.121 Safari/537.36 Edg/85.0.564.63

Steps to reproduce:

First the environmental details:
Thunderbird Version: 68.12.0 (64-bit)
OS: macOS Catalina Version 10.15.7

Now the bug:
Thunderbird does NOT handle nested HTML lists well - the example below is an unordered list nested in an ordered list, but ordered lists within ordered lists are also a problem.
I EXPECT that nested lists would be displayed as they would if the list were pasted into https://www.w3schools.com/HTML/tryit.asp?filename=tryhtml_lists_intro
Reproduction details below:

1. Compose a new message
2. Click inside the compose message area
3. Choose Insert > HTML
4. Paste the following:
   <ol>
   <li>Coffee</li>
   <ul>
   <li>White</li>
   <li>Black</li>
   </ul>
   <li>Tea</li>
   <li>Milk</li>
   </ol>
5. Click insert
   ==========================
   The nested un-ordered list causes the numbering sequence of the ordered list to FAIL - item 3. Tea SHOULD BE item 2. Tea
   The good news is that if the recipient has a well behaved email client (e.g. gmail) then the recipient's email will display the list properly.
   The bad news is that if someone sends ME a properly formed list, TB does NOT display it properly.

Actual results:

1. Coffee
   ° White
   ° Black
2. Tea
3. Milk

Expected results:

1. Coffee
   ° White
   ° Black
2. Tea
3. Milk

Now this is RIDICULOUS - when reading the bug, the page has NOT displayed my ACTUAL RESULTS AS TYPED - instead it has renumbered my ACUAL TYPED LIST. So will attach picture

Hey Chris, sorry for the inconvenience. It's a Core Layout bug (outside Thunderbird) which has already been fixed by Firefox. With a bit of delay, the fix will roll out in Thunderbird automatically.

This bug tracker (BMO) is using Markdown styling (see that small hint/link below the comment box?), so formatting your comment isn't ridiculous as such, but quite expected. Markdown is clever enough to actually fix the wrong list numbering which you wanted to show us and which this bug is all about... I do appreciate the irony of one system making correct lists wrong, and the other system making wrong lists right when you intend to present the wrong version... ;-)

Please be respectful and refrain from calling our "web site" (bug tracker) stupid whilst you're expecting us to handle the problem you're reporting using the very same bugtracker.

Have a nice day!