ajtruckle,

This is not a bug or feature request for MantisBT (you are asking for help on how to deal with problems of a 3rd party plugin). I am therefore resolving this issue as "no change required".

Please contact the author of the plugin to get support for it.

And why can't this new editor window be used on the Add Note window?

0022423 might be the reason for it, but please ask the author.

Yes that is the case for part of this issue.

But, MantisBT now supports Markdown and thus really, MantisBT itself needs to make this enhancement more user friendly. No one has any knowledge of it. No help links, no editing links. Users are blind to that.

That plugin went some way to resolve that but not far enough.

I would have thought that MantisBT wanted their own issue tracking system to be improved for this. I don't see anything being dealt with that quickly by the author. It seems he has only made that plugin available as is suited his company needs. He didn't think of the wider audience. I have absoluteoly no idea how to review / modify the plugin to make it work with other browsers. A pity.

But, MantisBT now supports Markdown

Markdown has been announced as "experimental", see https://www.mantisbt.org/blog/?p=498
That's why it's not activated in a default installation.
There are various other known issues, check all open issues with category "markdown" for it.