I’m already using WPFB-Pro as a mu-plugin so I can safely modify it where needed.
See: https://codex.wordpress.org/Must_Use_Plugins for more details

My issue is that I’m trying to include thumbnails for the WYSIWYG Editor Plugin file attachment tree. I think it would be a better user experience to preview the images before attaching them. Right now users can only see the names of each file.

How could this be achieved?