A common question that I hear from developers is “What is the market share of Firefox?” (or, more recently, “What is the market share of Firefox 2?”). There are a couple answers but generally you shouldn’t care about the results.

How do you determine the global market share of a browser?

It’s hard to give a proper answer to this – there are so many factors that go in to determining an exact global market share. How do you track users? If you’re tracking web sites, which web sites do you track? No matter how you look at it, it’s hard to pin these down.

The Mozilla Metrics team has been blogging recently, discussing different ways in which market share can be evaluated. In a recent post breaking down the various metric services they looked at some of the most popular ones, analyzing their quality of data.

One of the services that we make a lot of use of to get a decent global view of browser market share is Net Applications. Their data comes from a wide selection of sources and tracks over 160 million users.



Data for Feb. 2009.

When someone is wondering what the global market share numbers look like, I generally point them at the Net Applications data.

How do you determine the market share of a specific browser version?

Again, Net Applications comes through well. They provide a data breakdown of browsers by version that works well.

This helps to answer the question that I’ve seen recently: “What is the market share of Firefox 2?”



Data for Feb. 2009.

Thankfully the Mozilla Metrics team released a country-by-country breakdown looking at some of the locations where users are slowest to upgrade.

Why you shouldn’t care about these numbers.

The above global market share numbers should only matter to two groups of people: Browser vendors (it’s nice for them to be able to know how many people are using their applications) and generic tool developers (creators of libraries that could be used by any number of people in any locale). The problem is that most people don’t fall into either of these categories.

Instead, most developers should be monitoring one statistic: What is the browser share for my web site.

In order to make smart decisions about what browsers to support for your web applications you need to, first, get an accurate picture of what your users are using – any other determination will simply be incorrect and will give you a skewed sense of importance.

I talked about this balancing process last year, asking developers to balance the amount of work required to support a browser with the raw number of users that the browser provides.

I also talked about this balancing process in my recent talk at Yahoo!: The DOM is a Mess.

In fact, when determining what browsers to support for the jQuery library we use a mix of market share and intuition. We immediately support the major browsers – their current version, their previous version, and their next version. Additionally we extend support to older browser versions that still have significant market share (such as IE 6).

It’s important to note that the above data has absolutely no relation to the actual visitors to the jQuery.com web site. Developers tend to present a very skewed view of which browsers are the most popular:



(Visitor breakdown to jQuery.com, by browser, taken on March 29th 2009.)