ColorZilla – Eyedropper, Color Picker, Palette Viewer for Firefox

Features:
* Eyedropper – get the color of any pixel in the browser window
* An advanced Color Picker similar to ones that can be found in Photoshop and Paint Shop Pro
* Zoom option makes picking colors easier
* Palette Viewer and editor. Palettes fully compatible with GIMP.
* Webpage DOM Color Analyzer – analyze DOM element colors on any Web page, find out what CSS rules set the colors, locate corresponding elements
* Online Palette Viewer – allows viewing, bookmarking and sharing any color palette online, click here for an example
* History and Favorites palettes
* Page Pan option allows to quickly pan the page without using the scroll bars
* Displays element information like tag name, class, id, size, relative mouse position etc.
* Outline elements under the cursor
* Multi-platform – works on MS Windows, Linux and MacOSX.
* Manipulate colors by their Red/Green/Blue or Hue/Saturations/Value components.
* Auto copy the generated or sampled colors in CSS RGB, Hex and other formats.
* Launch the DOM Inspector or Firebug (if present) with the last selected element
* Measure the distance between any two points in the browser window
* Get the color of dynamic elements (hovered links etc.) by resampling the last sampled pixel
* Customize the Color Picker resolution to give the best performance vs color precision
* Can be hidden when not in use