I’m a little late with this one - I know, I know. So let’s not waste any time and jump right into it:

John Lilly, Mozilla’s CEO stated in late November 2007 that Mozilla assumes that Firefox has more than 125 million users. That was in November last year - about 8 months ago. In the meantime Mozilla released version 3 of Firefox to much fanfare - so I guess it is safe to assume that now significantly more than 150 million people all over the world use Firefox (you can download Firefox in about 50 different languages). That’s a global market share north of 20% - more than one in every five human beings on the net uses Firefox.

Now you should understand that Firefox is an open system - you can easily add extensions which do everything from the mundane (like displaying funny pictures) to turning Firefox into something completely different (like creating a kiddy-friendly browser). Extensions can speak to application servers to get things done in the background; they can skin the browser to make Firefox look, feel and behave different and they can interact not only with the web but also with other applications on your computer (take for example FoxyTunes which puts a little iTunes controller into your browser status bar). Firefox extensions are developed using JavaScript and XUL (XML User Interface Language) - which makes them easy to build and maintain (and often doesn’t require a steep learning curve as JavaScript and XML is heavily used in pretty much everything Web 2.0).

Now let’s bring this together:

We have 150m active users who experience the Internet through Firefox - they spend hours every day (!) in Firefox. We have a platform which allows us to build powerful applications (aka extensions) with little effort. We even have a working distribution system (Firefox features extensions in the application and makes it easy to download and install new extensions).

In my eyes this is one of the most amazing business opportunities around - and funny enough one of the least explored. We have tons of discussions about Facebook (even I blogged about it), we speak about OpenSocial and iPhone Apps - there are even VC funds specifically for Facebook and iPhone applications. But we seem to miss the great opportunity which stares us right into the face every time we open our browser.

Still not convinced? StumbleUpon built its business on top of a Firefox and Internet Explorer extension and was sold to eBay for $75m. The StumbleUpon extension was downloaded more than 8 million times according to the Firefox extensions website. The aforementioned FoxyTunes was sold to Yahoo for $20-30m, again FoxyTunes build its business on a Firefox extension. And it was download more than 7 million times…

As always I would love to hear your ideas and opinions - and if you happen to build a business on top of an extension: Let me know.