What are some alternatives?
ezLinkPreview - Browse more efficiently: Preview links and images without leaving your current tab.
Hover Zoom - Enlarge thumbnails on mouse over.
ImageZoomer - Zoom images inline on the current page by holding the right mouse button and scrolling the mouse...
Thumbnail Zoom Plus - The official site of the Thumbnail Zoom Plus add-on for Firefox
Shaarli - Shaarli is a minimalist link sharing software you can install on your own website
ImagePreviewer - This extension shows a popup with an image preview when hovering over link that points to an image file or a page with an image.