My Firefox extension PixelZoomer is now available for Windows: PixelZoomer for Windows is a free Windows®-based application that creates a desktop screenshot automatically and allows for pixel-based analysis.
The program comes with the same features as the Firefox extension so you can zoom into the screenshot, measure distances and pick colors. PixelZoomer for WIndows runs on Mozilla XULRunner and its program code is mainly based on the Firefox extension. The module for the screenshot creation had to be rewritten in C++ but could then be used as XPCOM component. The Windows version allows you to capture other browsers than Firefox only so you can check your website in all major browsers since the entire desktop is captured (support for multiple monitors is also included). You can download the application for free on the website. Have fun!