What’s the first thing that happens when you visit a video on YouTube? Ads pop-up on the video and the video automatically starts playing. All this takes place before the video loads completely and that can get really annoying. Joe Simmons has solved this problem by building a GreaseMonkey script for Mozilla Firefox.
This script buffers the video first before playing the whole thing. The ads within the YouTube video are removed, and the HD option is automatically turned on if that option is available using the script. You can download the script from Userscripts. You must have GreaseMonkey installed first for this script to work.