The growth rate of the Firefox browser is slowing, though that’s
exactly what you’d expect would happen when word of the browser is
spread virally. It’s got the base of first adopters, who quickly try
anything that is new, and now must pick up everyone else, which is a
lot harder against an entrenched competitor. I am guessing that it
stablizes around 10 percent without any further promotion. One thing we
know for sure: full-page New York Times ads, like the one Firefox
promoters ran, are demonstrably ineffective.
Take a look at WebSideStory’s analysis for a bit more information.