I am thinking of building a firefox extension.
This extension requires the ability of performing screen shots.
UPDATE: This feature has been removed from Firefox, unless you're writing a plugin. Please look for different alternatives, see http://badassjs.com/post/12473322192/hack-of-the-day-rendering-html-to-a-canvas and https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/drawWindow
Back in the days, you could: take a screenshot of firefox's window, yes, and it was so easy it hurt. You had to render it into a canvas. See https://developer.mozilla.org/en/drawing_graphics_with_canvas#Rendering_Web_Content_Into_A_Canvas
<canvas id='my-canvas'></canvas> <script> var canvas = document.getElementById('my-canvas'); var ctx = canvas.getContext("2d"); // Draw the window at the top left of canvas, width=100, height=200, white background // drawWindow has been removed :( ctx.drawWindow(window, 0,0, 100, 200, "rgb(255,255,255)"); // Open another window with the thumbnail as an image open(canvas.toDataURL("image/png")); </script>
If you mean a screenshot of the entire desktop, I don't think so