Preview in Gnome File Chooser

Anyone know of a way to enable any sort of image preview in Firefox's "File Upload" dialog in Linux w/ Gnome?  File choosers for some Gnome applications, such as the GIMP or the wallpaper chooser, show a preview for images.  I've tried asking elsewhere, but they all just get confused as to why I would have so many images with only numbers in the file names (damn you 4chan!). 
In b4 opera and possibly Gentoo.

>>9
How often do you use Realplayer or Quicktime?

How often do you use a file dialog?

Exactly.