Edited version of Crunchyroll Black for users that have trouble with it working on Firefox 3.5.
Turn Crunchyroll's background to black "RGB(0,0,0)". Also adjusted link colors. Edit your own link and background colors with the RGB values. =)

Works with Chrome extension, ChromeStylist too.

Name: Whatever-you-want

Match pattern: ^http://www.crunchyroll.com/

Stylesheet text:

*{background-color:rgb(0,0,0) !important;
color:rgb(180,180,180);}
/* For links: */
a:link{color:rgb(100,100,100) !important;}
a:visited{color:rgb(0,0,200) !important;}