Rated 4 out of 5 stars

Great concept, with a few minor niggles: Delay should be specified in milliseconds instead of seconds (250-500ms, I think, would be ideal for me), throbber.gif has ugly white ridges that clash with darker Windows themes (http://tinyurl.com/32nd4ww), and the panel should respect the user's page zoom setting (I browse at 200% zoom on my TV using "NoSquint", and because Thumbnail Zoom displays images 1:1, they often appear smaller than the original thumbnail). When these issues are resolved, I'll gladly upgrade my rating to five stars!

This review is for a previous version of the add-on (1.3). 

Hi, we changed the delay field to support comma values and we fixed the throbber issue with dark themes. Also we now support the user's page zoom settings. Thanks for your feedback!