Haochi has created a Greasemonkey script, that once installed, will let you preview YouTube video by simply mouse over “image thumbnails”, without clicking on the link itself. The script acts same like as Snap Shots for previewing YouTube videos, but doesn’t annoy the heck out of you, and you can turn it on for websites of your choice like Digg.
The script’ll is really handy for Firefox user, who browse Digg like site with YouTube image thumbnails posted. To get it work, you must’ve Firefox and Greasemonkey script installed on your system.
You can download YouTube Preview script here.