1. Click extension's icon 2. If design.png exists, it will be placed over the page. 3. If there is no design.png file, just drag and drop image onto the page – image will be placed over. 4. To change opacity use left click and right click. 5. To remove image placed over page, click extension's icon. Image is centered horizontally on a blue translucent background. The width of the superimposed image in pixels displayed in the Developer Tools console. Change the width of the window is conveniently with Developer Tools enabled - in this case in the upper right corner shows the size of the window in pixels.