Firefox prefetch

Are you aware of the effects of the network-prefetch-next preference in Firefox? It’s actually quite an old feature (according to this site it was introduced way back in 2003), but I’m pretty sure not everyone know the possibly scary side effect of this smart(tm) feature. It tries to make the browser being one step ahead of its user, by prefetching sites it assumes the user will click on next.

This is what’s being logged on honeynor.no when I (84.215.x.y) google the word “honeynor“.

84.215.x.y - - [18/May/2010:23:42:55 +0200] "GET / HTTP/1.1" 200 17832 "http://www.google.com/ \
search?hl=en&source=hp&q=honeynor&aq=f&aqi=g-s1g-sx7&aql=&oq=&gs_rfai=&fp=64bbd6d9727d98e0" \
"Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.3) Gecko/20100423 Ubuntu/10.04 (lucid) \
Firefox/3.6.3"

I haven’t left google yet!, but my very intelligent browser thinks I might click on the first link (www.honeynor.no) so it goes ahead and access the site, way before my puny brain has had any chance on processing the search output. In true PKD-style, I hereby accuse firefox of a precrime!

Why is this action bad? Let me answer the question with a question; Do you always want to access the sites presented to you when you search the web? I can think of several cases where I’m not keen on letting some third party know of my interest in them; either that’s during an analysis or in case of possible repercussions against me for accessing a site in an unexpected or socially engineered manner.

It seems google is in cahoots with firefox on this one, because I’m unable to reproduce the same result using bing, yahoo or alltheweb. Only on google is the prefetch mechanism activated.

So, how can you disable this feature? Luckily it very easy; go to about:config in your firefox/mozilla browser and set the parameter network.prefetch-next to false. That’s it!