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
Hover for Safari - Hover for Safari allows you to expand any image, link, or GIF just by hovering over it.
RedReader - RedReader - An unofficial open source Reddit client for Android.