When you ask Firefox users what their favorite extension is they’ll commonly say Adblock Plus. It’s currently the second most popular extension on the add-ons site, and receives over 250,000 downloads every week. With numbers like that you’d expect the extension to be installed on nearly every copy of Firefox, but that’s not the case.

What I found out when I released CyberSearch was that any developer can choose whether or not they want the download stats of their add-on to be publicly available. Even more interesting is that anyone can go to this page to see a full list of extensions whose stats you’re able to view. Naturally I was curious how many people were using the Adblock Plus extension.

As of July 30th there were 4.42 million active daily users of Adblock Plus. In mid-July it peaked at 5.5 million users, and over the last year the number of people using Adblock Plus has been rapidly growing:

Number of Active Adblock Plus Users from July 2007 to July 2008
adblock users.png

How does this stack up against the number of Firefox users? The last time Mozilla reported on how many Firefox users there are was when they were going after the world record for the number of downloads in a 24-hour period. They said that there are 180 million users worldwide, which means about 2.5% of all Firefox users have Adblock Plus installed.

There are some other things that need to be considered, such as alternative ways to block ads (other extensions, Greasemonkey scripts, etc…). I’d also assume that heavy Firefox users will be more likely to have some sort of ad blocking system installed over those people who just get on once or twice a day to check their email.