Review Updated:

Works as advertised. My earlier review complained of autoplaying not working. Just give it 2-3 seconds as it starts to play your video (to enable buffering), stops playing, seeks to very beginning. This happens seamlessly as you're browsing in another tab or so.
Job well done. Now I can come back after 1 hour and see my video and not have to deal with dialup any more.

Given the choice between using this script and the two other good scripts for YouTube, I personally choose to use this one. I really like the simplicity and cleanness. It does exactly what I want and doesn't overdo things.

This script does nothing at all and there's no way to configure it. Greasemonkey is enabled and so is the script and I've restarted FF (3.5.2) since.

[EDIT]: Works great with the latest update. The ability to automatically play in HQ saves a fair bit of hassle.

I hated when Youtube videos always started up automatically as soon as you went to them. With this script, I don't have to stop the video when it starts up to let it buffer, and I like how it buffers without starting the video.

one of the main reasons I stick with firefox...
5 stars for sure.

My thanks to the author. I've been wanting something like this!

I haven't had any problems or glitches since I installed.

IT DOES BUFFER AND IT GETS THE HD VERS IF AVLB.

Compatible w/ Google Chrome

Thanks, I've been wanting this!