Excellent addon :) Rated 4 out of 5 stars

Hi, I'm trying to download a ~ 2 hour video from youku with Media Stealer. It does download each part, but when it completes and moves on to the next part, the status says interrupted instead of completed. And right now, a completed part is getting downloaded again, for apparently no reason.

Another question I had is, does this addon download in parallel or does it save the stream as it is coming in? I mean, does MediaStealer download the video seperately from the player?

This review is for a previous version of the add-on (1.2.9). 

When watching youku, it actually uses several parts. Each part is downloadable and playable when using a media player.
Despite being "interrupted", chances are the file will be still readable by the operating system. Try it and you'll see. Sometimes it takes a little longer until it says "finished".
Media Stealer downloads the video separately from the player, there's no need to keep the tab of firefox open. (except when there are multiple parts)
The next version 1.2.9a will resolve a small bug regarding completion of files. Until then, I highly recommend to change the downloaded filename, it ensures no data will be overwritten.
Media Stealer 1.2.9a can be downloaden from this website: http://code.google.com/p/mediastealer/downloads/list
Media Stealer 1.2.9a is currently not approved by Firefox.