[e3fnxs6p]

Currently, when "first image in post" (source2) is set, it won't display thumbnails from attachments. When "first attachment" (source1) is set, it won't display thumbnails from the first image. But often, you would like to have a combination of these options, instead of excluding each other.

You can solve this by doing this:
1) set the thumbnail source to "First Attachment".
2) go to plugin manager > "Forum Display - Threadbit Display" > find the line containing
$hook_query_fields .= ", MIN(attachment.attachmentid) AS attachmentid";
and append under that line, the following line:
$hook_query_fields .= ", thread.thumbnailurl AS thumbnailurl";

That's all.