Currently Thunderbird has the option to "Automatically mark messages as read", either immediately or after a small delay.
I would like to request a third option: "When clicking or scrolling"
I have the preview pane open and usually cycle through my messages, then stay on a given message, but that doesn't mean I've read it. So the more strict option 'after displaying for xx seconds' still sometimes falsely marks emails as read.
However, opening the message, clicking (a link, select text, etc) in the preview pane or scrolling in the preview pane actually indicates I've interacted with (or 'read') the email.