Works great but...... Rated 5 out of 5 stars
It works great -- extremely fast, easy and seamless. But, as someone else said, it would be even better if we could specify where to save the clip. I now have to locate the clip in my crowded download directory and manually move it to My Videos. If it wasn't for that, it would be perfect!
LATER: Just installed the latest version and it works like a charm; absolutely perfect now; thank you, thank you, thank you. Now it is 5 stars all the way!
Check the latest version (1.7.16): https://addons.mozilla.org/en-US/firefox/addon/download-youtube/versions/
The extension now shows a "save as" dialog.