Alexa.com, the "web information company" is designed to provide statistics on the popularity of websites on the internet - I just wonder how accurate it is at doing so.
Alexa gathers its statistics using the Alexa Toolbar which is an add-on to Internet Explorer. There's the first problem - there's no official Firefox version. (I say official because there is this Firefox extension, but I'm not convinced that it sends home browsing statistics). I think most would agree that the more savvy web user will tend to use Firefox in preference to IE... and they'll sift through more of the web than the average surfer. But, being affiliated to Amazon.com, you'd think it would have enough users to provide statistical reliability anyway. I guess the more popular you website is, the more reliable the figures are. (Other problems include extra browsing lag and occasional crashes.)
So what percentage of internet users are estimated to have the Alexa Toolbar installed? Alexa doesn't say. On the basis of Nimisis.com's numbers in the last few months, I would guess that it's about one in 600. Not a lot. Still, this will no doubt vary according to the country, among other variables. Below are some graphs for Nimisis.com and you can see there is some correlation.