If your web hosting account is low on bandwidth, you might want to consider blocking use of the Firefox extension called Fasterfox. By adding a blurb to your robots.txt file, you can block this extension.
http://www.skattertech.com/2006/02/how-to-block-fasterfox-requests/ http://digg.com/programming/HowToBlockFasterfoxToSaveBandwidth
Be sure to read all the comments from both the above articles; it gets very interesting.