No more Flash on YouTube but major memory leak and high CPU usage Rated 3 out of 5 stars
I agree with the greater part of what @TrueBlue1981's review wrote in his/her review. When YTC is enabled, Firefox freezes quite often and actually everytime you open a new YouTube video. This applies to an even greater extent if you have enabled the "lights off" setting by default (all but the video frame turns darker so that you don't get distracted by the rest of the content on the current page). There also seems to be a heavy memory leak, which also means that there is a major secuirty risk with this addon. There is also a major increas in CPU usage when playing YT videos, while YTC is running. Even greater than using the standard Flash player I might add.
However despite all that it does offer a couple of neat features and that is why I give it 3 stars. The greatest of all is the HTML5 wrapping feature that enables you to play videos in HTML5 video format (+1 star). This is a huge deal for Linux users because Flash player for Linux is complete garbage. Another cool feature is the large set of aspect ratio and player sizes, allowing the user to tweak the player according to the video itself AND to the display he/she is watching it on (+1 star). You are also able to tweak many other things. (+1 star)
If the bugs are fixed, YTC will definitely get 5 stars from me.