I looked into including the firefox logo, but according to the guidelines at: http://www-archive.mozilla.org/foundation/identity-guidelines/firefox.html, the logo can only be displayed on solid white or black background, no mid-tones or strongly colored backgrounds. Since I can't guarantee the style or color palette of the site it's installed on, I decided to leave it off. My guess is that a significant number of Joomla sites would probably have something other than pure black or white for the module background.