HOW TO : Stop Auto-play In YouTube Videos
1. TubeStop is a Firefox addon which stops the auto-play feature of YouTube and let them load fully first to play.
Download the TubeStop Firefox Addon --> https://addons.mozilla.org/firefox/downloads/latest/6648/addon-6648-latest.xpi?src=addondetail
2. Well, not everybody uses the Firefox browser. So, here is another method for other browsers including Firefox.
YouTube Prevent Autoplay is a script which prevents videos from playing automatically by replacing the default YouTube player with the YouTube player that doesn't support auto-play.
Download the YouTube Prevent Autoplay Script --> http://userscripts.org/scripts/source/12008.user.js