Hover Zoom - Enlarge thumbnails on mouse over.
Hover Zoom+ - Google Chrome extension for zooming images on mouse hover - extesy/hoverzoom
Image Max URL - Help find larger or original versions of images, including a customizable image popup feature
Thumbnail Zoom Plus - The official site of the Thumbnail Zoom Plus add-on for Firefox
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.
RedReader - RedReader - An unofficial open source Reddit client for Android.