keepvid.com is a nice, useful alternative tool to widgets/add-ons download tools like I usually use in Opera and Firefox to download videos from You Tube. You don't have to install anything from keepvid.com. Simply past link to your video and it'll download it straight to your computer.
You can even choose video quality between .flv which is low and .mp4 - high.
It's very simple, easy and safe and works with any web browser.