One of the persistent pieces of “common knowledge” out there is the idea that Firefox is slowly grinding Internet Explorer into the ground. Along with this “common knowledge” is the assumption by some Web developers that since the Firefox Revolution is nigh, there is no real reason to take Internet Explorer into consideration. Sadly for the Firefox fans out there, this simply is not true.

Where does this piece of “common knowledge” come from? A lot of people point towards IE’s declining market share, FF’s rising market share, and FF’s current market share of about 30%. However, the people who point to these numbers are definitely failing Statistics 101. As I said in June 2006 (“Be Careful That Your Data Does Not Lie”), first order numbers, are not very useful, and are essentially worthless without at least some baseline numbers to be compared to.

Having been curious about this for some time, I decided to see if Firefox’s adoption rates were the stuff of legends or not. And I have found that Firefox is indeed not a superhero, but an average Joe.

Using W3School’s month-by-month browser market share numbers, I came up with some startling facts: Firefox’s market share growth (and indeed, the entire Gecko family’s market share growth) since the introduction of Firefix is actually less than it was before Firefox was introduced.

Here is my chart of calculations:

The Pre-Firefox velocities and accelerations are based on 12 months of data, and the Post-Firefox numbers use 21 months of data.

Note: I recognize that these numbers and conclusions may be controversial; as soon as I can (technical issues), I will make the full spreadsheet available for download. I will also be more than glad to use alternative market share numbers from a different source, as long as the alternate source measure a large sample of users and is of a “general purpose” interest, to avoid potential skew caused by a niche audience.

[Added: 9/29/2006: Download the spreadsheet]

What is happening? Well, what you are seeing is that the velocity (rate of market share growth) is lower for the Gecko browsers in the 21 months after Firefox came out than it was in the 12 months before Firefox. To eliminate any doubt, I broke the numbers out into Firefox and Non-Firefox Gecko browsers, to show that it is not simply Netscape or Mozilla destroying the numbers.

What we see in these numbers, is that while the bulk of IE’s market share loss since FF came out is due to FF, that loss rate is smaller. More important to note is that Firefox came out of the gate with a 16.6% market share in January 2005, and the Gecko market share was at 18.4% in December 2004. In other words, Firefox quickly supplanted the other Gecko browsers, and as Firefox immediately became the “face” of Gecko, Gecko’s growth rate wilted. Or to put it even more simply, Firefox is not as attractive to users as Mozilla and Netscape were.

I was suspicious. The numbers just did not jive with what “common knowledge” was. Indeed, I had bought into the idea that Firefox had great accelerated IE’s demise myself. I thought that maybe the numbers were off, but many sources report the 30% number (give or take a few percentage points) as Firefox’s current market share as well. And I have never heard anyone argue against W3School’s numbers in the past. I thought that maybe Firefox’s immediate 16.6% market share in January 2005 seemed wrong, so I checked Firefox’s site to see when it was officially released as Version 1.0: November 4, 2004. so yes, the W3School numbers do not break out Firefox as a separate browser for two months initially. But even that seems pretty irrelevant; the raw numbers do not show Gecko’s market share growing by more than 1.6% in any of the months between July 2004 and January 2005; and the 1.6% number is in November 2004. So even accounting for the fact that Firefox was being rolled into Gecko for some time, which did cause a slight spike in Gecko market share capture, it is difficult to say that Firefox is driving adoption of itself, or causing IE’s demise.

At best, we can conclude that while it was bound that non-IE browsers would eventually hit the “glass ceiling” of people who will never leave IE, it may have raised that ceiling a bit.