Hide certain folder

Hi! I have another extension that creates a "thumb" folder with thumbnails inside every folder I add.

What I want is to hide every folder with this name. What file should I edit to achieve this? And how? If this is not possible maybe there is a trick to show only the first level child folders, so that when I create a FILEman gallery my site will show me the sub-folders and only the files inside them.

Thanks in advance!