We stopped by Mozilla's booth at MWC today, and in addition to all the Firefox promotion the company's doing, it was also showing off something a little different: its Boot to Gecko project. Boot to Gecko is, in essence, a phone operating system that is entirely web- and HTML5-based. From the moment you turn the phone on, everything you see is HTML5. Even the dialer uses Mozilla's "telephony APIs," and is itself web-based. There are no native apps, just a series of the most impressive bookmarks you've ever seen.

We got to use an early version of Boot to Gecko, running on a flashed Samsung device that used to run Android, and we were really impressed. The operating system's not totally smooth — reps told us over and over that "this is a project, not a product" — but apps worked as advertised. Sending messages, taking pictures, playing Cut the Rope, browsing the web, and nearly everything else we tried worked correctly, if not always gracefully. It was actually really hard to believe that we were using an entirely web-based device — we kept asking if they were lying, and it wasn't really HTML5. Of course, there was an easy way to prove it: you can see the source code of any app at any time, to see exactly what's behind what you're seeing.

The possibilities for this kind of device are fascinating, particularly with cheap, low-powered phones. Since so much of the processing is done on the web, effectively all your phone would need to have is an internet connection and a halfway decent processor (and probably a lot of RAM) to run Boot to Gecko.

Update: apparently we were given a bit of incorrect information about offline capabilities. Here's what Mozilla developer Vivien Nicolas had to say: "Right now, without a data connection, you can receive and make both phone calls and SMS messages as well as use any of the applications that have already stored their data on the telephone (including applications like the photo gallery, the camera, and the video player). Games such as Cut the Rope, however, are not stored locally and are not currently available without an internet connection. Web authors are able to use existing web technologies, such as the application cache, to enable offline access to their applications."

The version of Boot to Gecko currently has one fatal flaw: nothing works offline. That means when you're not connected to a cellular network, you literally can't do anything on your phone. But Mozilla said its and HTML5's technology support choosing apps and data to make available offline, and that it's working on enabling that. Mozilla's also working on a Marketplace, which will let you add apps to your phone and use them in the browser; through Boot to Gecko's Persona feature, your apps and data would then be synced across every device using the platform.

The other challenge for Mozilla could be getting OEMs and carriers to use yet another operating system. But Mozilla already has one partner, Telefonica, and says it's working with many more. We're not sure this is the OS of the future, but it's an insane testament to how powerful HTML5 is, and how much we can really do when we're online.