We all know that add-ons are one of the best things about Firefox and Firefox users love their add-ons. However there was never any clear data on the add-ons installed untill Firefox 4. In Firefox 4, a new feature was introduces which allows Mozilla to keep track of an aggregate of add-on usage in Firefox.

Mozilla has released the data they have collected and according to that, 85% of the Firefox users have add-ons installed. That is a huge number – much higher than the previously believed 66%. This number does not include the add-ons that comes bundled with Firefox. The 85% consist of only those who have installed at-least one add-on on their own.

Here is a graph showing the add-on usage and the number of Firefox 4 users:

Another interesting data that Mozilla has released is the distribution of the number of add-ons installed. According to the data, an average Firefox user has five add-ons installed. And, there are more number of people with two add-ons installed than those with only one installed.

Here is the distribution of the number of add-ons installed:

How many add-ons do you have installed in Firefox?

source: Add Ons Blog