wrong URL in <img src= attribute

my files are in /files and that works fine as long is a don't want to click on any thumbnail to display the full image.
The Thumbnail-URLs are build correctly but the full-image-URLs are with sites/default/files and this does not work for me.
The Problem is in Line 423 of fast_gallery.module where this folder is hard-coded.
I patched the file so that it works for me. I don't know if that is right for all other installations.