On all sites? I wonder whether you have a setting that conflicts with how this extension works. Generally speaking, it creates an HTML canvas the same size as the image and puts the image on the canvas, then extracts a blob object that it can save in your choice of formats. Similar to screenshotting. If you want to try some troubleshooting, you could use either contact method on the main listing page: (1) email, or (2) create an issue on Github.