Thumbnail Zoom Plus is a Firefox plug-in which shows a full-size image pop-up  when you hover over a thumbnail or image link.  When you hover your mouse over a thumbnail or an image or video link, the  add-on displays the full-size image or video still-frame in a floating window.  Supported sites include Amazon, Bing, Facebook, Flickr, Google, IMDb, LinkedIn,  Netflix, Pinterest, Reddit, Tumblr, Twitter, Yandex.ru, YouTube, Wikipedia,  WordPress, Yahoo Images, and many more.