Up to 13% worldwide, showing 16% in the USA — and there’s very little doubt in the stats about which browser Firefox is winning adherents from.
One in six is easily enough to cross many managers’ population “10% limit” for electing to support a particular browser model, so Firefox support (or — more specificially — HTML standards support) should soon start arriving at many sites which are currently welded to supporting only a single proprietary (and in many ways odd) browser family.
This ought in turn to make life easier for Konqueror/Safari, Opera and all of Firefox’s conceptual siblings simply by widely introducing compliance to standards (or at least something within calling distance of standards) in place of much HTML esoterica aimed at the vagaries of one closed web-browser’s ideas.
This may not be obvious to non-programmers but what it means in practice is that many programmers will (for the first time, in many places) actually know what basis upon which to test their code (such as web browsers & various automata) instead of simply guessing with and/or iterating over an alien-looking test-bed setup until it appears to work — kinda, sorta, most times.
This will work positively in at least two directions, since Firefox also gives the website designers a relatively simple, portable, freely-available way to test their own code compliance.