When Mozilla releases its Firefox 3 browser update June 17, it hopes to set the first-ever Guinness world record for number of Internet software downloads in 24 hours. The target: 5 million. That would be quite a feat, since the last Firefox update netted just 1.6 million downloads. But it's no mission impossible. Firefox 3 speeds up browsing and adds a host of improvements, including the ability to adapt to your preferences as you use it. Over the past half-decade, Mozilla, an open-source software company, has gained grassroots support from some 170 million users and amassed an 18% worldwide market share, according to Web metrics outfit Net Applications. In the process, it has broken Microsoft's (MSFT) grip on the critical browser market.

Yet just as Mozilla girds for download madness, Web browsing is entering a new phase: It's about to explode on cell phones. Until now, mobile browsing has been frustrating—slow, text-heavy, and hard to navigate. But improvements in software, processing power, screen size, and networking bandwidth are expected to boost the number of high-performance browsers on new mobile phones from 76 million last year to 694 million in 2013, according to market researcher ABI Research. "There's a lot of action to come," says ABI analyst Michael Wolf.

Not to be left behind, Mozilla is readying a mobile version of Firefox 3 for release later this year. One of its aims is to make it easy for people to shift from browsing on their PC to browsing on their mobile and to pick up where they left off. "There's a lot of room for helping people get to Web sites and have rich browsing experiences," says Jay Sullivan, head of Mozilla's mobile initiative.

STEERING THE USER

Mozilla's impending entry into mobile browsing highlights the stark differences between the PC and mobile-phone worlds. Desktop browsing was ruled first by pioneer Netscape Communications (TWX) and then by Microsoft, whose Internet Explorer captured a 95% market share before sliding to 74% today. The mobile browser market is fragmented, in part because telecom carriers, handset companies, and software makers all have a say in which browser technologies end up on phones. Chaos rules, with dozens of mobile browsers in use. Norway's Opera Software is the leader in advanced browsers for smartphones, while Silicon Valley's Openwave (OPWV) is the leader in low-end browsers. Only one thing seems certain: No company will dominate the way Microsoft once did in PC browsers. Even Microsoft seems reconciled to the situation. "It's about the consumer choosing and us not dictating," says Scott Rockfeld, a Microsoft group product manager.

Browser software doesn't generate much revenue. Mozilla collects fees from search companies for embedding their search in its browsers. But browsers matter strategically to companies because they're the means by which users navigate the Web. If one company dominates, it can influence where people go and what they see. Browsers also matter tremendously to consumers because they have a major impact on their Internet experiences.

Right now the vast majority of mobile browsers are text-only programs that tap into limited Web sites designed especially for mobile phones. Apple's (AAPL) introduction of the iPhone a year ago showed that graphics and easy use could be achieved on a handset. Now competitors are racing to match or beat the experience on the iPhone, which uses Apple's Safari browser. Apple continues to race ahead, having just announced a new iPhone with faster networking. Each player has its own approach. Opera, for instance, enables people to access normal Web sites and zoom in on information that particularly interests them. Nokia (NOK), the leading handset maker with a 40% worldwide market share, uses different browsers for different types of devices. "There are a lot of options," says Ari Jaaksi, a Nokia vice-president.

ADVANTAGE: MOZILLA

The uncertainty about which technologies will eventually triumph leaves Web site operators, handset makers, and telecom carriers stuck making difficult decisions about which technologies to offer. For consumers, that means trouble. Some Web sites are a breeze to navigate via cell phone, while others are nearly impossible. There's pressure on the industry to adopt standard technologies that would improve compatibility between browsers and Web sites.

This gives Mozilla an advantage. Firefox is designed to work smoothly with other open-source software, and open-source technology is emerging as a popular choice for handsets because companies can share the costs and results. Last month, Mozilla became the first browser specialist to join the LiMo Foundation, a consortium of industry leaders that are collaborating on a mobile-phone software package that is based on the Linux operating system. However, Mozilla's new browser isn't included in Google's (GOOG) open-source software package for mobiles, called Android. For Mozilla, this next chapter in Internet computing will entail fierce competition on multiple fronts.