It drives me crazy that YouTube videos start playing automatically.
All I did was convert it into an extension for people that don’t use greasemonkey.
All of the credit goes to Yansky for figuring out this method.
I assume he used Fry’s 7-leaf clover.
Note that if you use this extension you really don’t need the other solutions.
After installing this extension, you’ll notice that the video is completely gone from the page.
Once you go for the video, it will then load and then start playing.
Download FlashBlock Extension from mozdev.org