thumbnails size from program

Hello,


The thumbnail size of my pictures in the finder is fine (use of "view" "show status bar")
But when I am online and from a program I want to select pictures from my computer, they are very very small. I do not want a preview of one only at a time (select pic + space bar) I want all the thumbnails bigger so I can do a multi selection.
Thank you.... soooooooo frustrated !!!