Mozilla is a nonprofit whose goal is to promote the web. So it is very important that this runs well on Firefox, Chrome, and on all other modern browsers - if it didn't, this would be pointless for Mozilla to do.

Mozilla helped out here, but the goal is to show that games on the web can be fun, and of course that means anywhere the web can run, in any browser.

edit: the distinction is also noticeable in that this is the Humble Mozilla Bundle, and not Humble Firefox Bundle.

Well, Mozilla is Humble's partner for this bundle, receiving a cut of the revenue, and asm.js is their work.

Plus, Chrome users can benefit from Mozilla's work, too, just as Firefox users may appreciate Google. It's the "Mozilla Bundle", not the "Firefox Bundle", after all.

In addition to some money going to mozilla, asm.js was also designed by mozilla.

My guess is that, while the games technically run on chrome, they require the asm.js optimizations that only Firefox has atm in order to run at a decent speed.

Some of the money is going to the Mozilla Foundation.

Some of what you pay goes to the Mozilla Foundation by default.