» Download Greasemonkey 1.7.1 (tested & works fine with Firefox 21.0)
» Download Greasemonkey 0.9.5 for Firefox 3 - 5
To stop Youtube Autoplay (pre-buffering allowed), download
YousableTubeFix.
If you can't download, click links below.
version 1.7.1
version 0.9.5