Does anybody know how Tbird 2 parses text into tables on a reply?

When I reply to a message, there are colored bars which seem to
indicate how many ">>>" levels there are in various portions of
text of the incoming message.

However, it also sometimes creates tables with red boxes around
the text, so that when I try to drag the mouse over various parts
of the previous message, it may or may not highlight, it's very
difficult to edit-down the text of the incoming message.

Is there some way to modify this parsing of the incoming message?

TIA!