How can I change the wallpaper on a Firefox OS device?

I have recently been learning about Firefox OS/B2G. I am aware of the extensive set of APIs in place that are able to fetch images from the wallpaper gallery, change settings and set reminders (to name a few). However, I'm completely stumped as to how to how to change the wallpaper, or, indeed, if this is even possible. Apologies if this is a silly question. Many thanks in advance.

You can do this by using a share activity

// imgToShare is the image you want to set as wallpaper
var shareImage = document.querySelector("#share-image"),
    imgToShare = document.querySelector("#image-to-share");

if (shareImage && imgToShare) {
    shareImage.onclick = function () {
        if(imgToShare.naturalWidth > 0) {
            // Create dummy canvas
            var blobCanvas = document.createElement("canvas");
            blobCanvas.width = imgToShare.width;
            blobCanvas.height = imgToShare.height;

            // Get context and draw image
            var blobCanvasContext = blobCanvas.getContext("2d");
            blobCanvasContext.drawImage(imgToShare, 0, 0);

            // Export to blob and share through a Web Activitiy
            blobCanvas.toBlob(function (blob) {
                new MozActivity({
                    name: "share",
                    data: {
                        type: "image/*",
                        number: 1,
                        blobs: [blob]
                    }
                });
            });
        }
        else {
            alert("Image failed to load, can't be shared");
        }
    };
}

You can test a live example with the Firefox OS boilerplate https://github.com/robnyman/Firefox-OS-Boilerplate-App/ .