Grab Color Palettes From Your Current Page In Firefox
Install it, and Palette Grabber sits in the left corner of your status bar waiting to leap into action. A single click (right or left) exports a selective palette based on your current page in Firefox. Palette selection is very intelligent, producing accurate swatch sets for each of the websites I sampled.
Palette Grabber supports several file formats, including Photoshop, Flash, Fireworks, PaintShop Pro, the GIMP, and Mac OS X Color Picker. Minimalists and power users can elect to save a tabbed text listing of RGB values.
For a 25k download, Palette Grabber is definitely worth adding to your Firefox install if you do any digital design work.