Palette Grabber by  Konstantine Prevas is a Firefox extension for web designers. It adds an “Export color palette” command to your Tools menu; selecting this command will extract a color palette for the current page and export it to a Photoshop/Illustrator color palette file. It’s useful for creating mockups of new designs which share a color palette with an existing design.

Palette Grabber supports Photoshop, Flash, PaintShop Pro, GIMP, Adobe Fireworks, and Mac OS X Color Picker palette formats.