Browser Backgrounds is a sweet Firefox extension for some looks makeover. It allows you to add any image as firefox browser background wallpaper. Be it a celebrity image or your favorite sports pic – you can them all as Firefox background using this extension.
You can create separate collection of photos for different type of images. Later you can also add more images in different collections and use them as Firefox backgrounds. As pointed by Jkwebtalks, make sure you resize images as per screen resolution before adding them to collection to be used for showing background image. Download Browser Backgrounds