A common pattern for using afw.display is to display an image with a zoom level. With the Firefly backend, currently it is necessary to mtv (display) the image and then issue a zoom command. This displays the entire image, which can take some time for large images, and then applies the zoom. This improvement is for the backend to keep track of the last commanded zoom level, and to include it in the call to FIreflyClient.show_fits.