] Below we will propose a new application architecture
] based on the Gecko Runtime Environment (GRE), which can
] be shared between separate application processes. Before
] discussing the rationales and trade-offs, here are the
] implications and key elements:
]
] Switch Mozilla's default browser component from the
] XPFE-based Navigator to the standalone Phoenix browser.
]
] Develop further the standalone mail companion application
] to Phoenix already begun as Minotaur, but based on the
] new toolkit used by Phoenix (this variant has been
] codenamed Thunderbird).
]
] Deliver a Mozilla 1.4 milestone that can replace the 1.0
] branch as the stable development path, then move on to
] make riskier changes during 1.5 and 1.6. The major
] changes after 1.4 involve switching to Phoenix and
] Thunderbird, and working aggressively on the next two
] items.
]
] Fix crucial Gecko layout architecture bugs, paving the
] way for a more maintainable, performant, and extensible
] future.
]
] Continue the move away from an ownership model involving
] a large cloud of hackers with unlimited CVS access, to a
] model, more common in the open source world, of
] vigorously defended modules with strong leadership and
] clear delegation, a la NSPR, JavaScript, Gecko in recent
] major milestones, and Phoenix.

And much more interesting reading. The future of non-Microsoft web browsing appears to be split between Mozilla/Gecko and the camp at Opera.

Mozilla Development Roadmap