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.
Please add imgflip.com, thanks.
Sample Reddit post which leads to here with the image being here.
The URLs sometimes have extra content, which you can remove. Just append .jpg to the end of the URL's ID.
A sample Reddit post with extra text at the end of the URL, which leads to here, with the image here.