I am running into this too.
http://castlerockconstruction.com/2013powergallery/galleries/ribbon_lightbox/index.php?gallery=15&theme=light
I want it to look like screen shot from Firefox, using Firebug to edit the common css file.
http://castlerockconstruction.com/2013powergallery/galleries/ribbon_lightbox/css/common.css
I am changing to 350 pixels wide. I appears I have changed it but not getting the result I want.
Thanks as always.