Latest version didn't fix Rated 4 out of 5 stars
Downloading the latest version didn't fix the issue for me, still brings up an empty web page. Edit: Nevermind, suddenly it started working. Though I'm wondering why 1080p is no longer available as it says in the description?
Edit: Ah, I see. That sucks. :/
Some explanations here: http://googlesystem.blogspot.com/2013/10/youtube-drops-support-for-1080p-streams.html
Basically, this extension only downloaded files from youtube.com and YouTube no longer provides URLs for 480p, 1080p or better. The YouTube player uses separate files for audio and video and these are the only files available for 480p and 1080p, but they need to be merged and that's a task for an advanced application like ffmpeg.