A first look at Firefox 3.0

Mozilla has officially released the first public alpha build of Firefox 3.0. Codenamed Gran Paradiso, Firefox 3 includes the new Gecko 1.9 rendering engine which leverages the open source Cairo rendering framework and features heavily refactored reflow algorithms that improve Firefox layout functionality and resolve some long-standing CSS bugs.

The reflow improvements in Gecko 1.9 (included in the latest Gran Paradiso nightly build, but not the alpha release) finally enable Firefox to pass the Acid 2 test, a CSS test case developed by the Web Standards Project to illuminate flaws in HTML/CSS rendering engines. To pass the Acid 2 test, browsers must comply with W3C standards and provide support for a wide variety of features that are considered relevant by web designers. The Acid 2 test has been passed by several other browsers, including Safari, Konqueror, and Opera, but not Internet Explorer. Passing Acid 2 is considered to be a significant milestone in Firefox development.

Left to right: Acid 2 under Firefox 2.0, Firefox 3.0 Alpha 1, and Firefox 3.0 Alpha Minefield (nightly)

Gecko 1.9 also includes a new threading model, support for Cocoa widgets on OS X, and some unit fixes (still under development) that could eventually facilitate a full-page zoom feature like the one found in Opera.

Firefox's transition to Cairo is significant. Written in the C programming language, the versatile Cairo graphics library is a vector-based drawing API that supports a wide variety of backends. Cairo can take advantage of hardware acceleration where available and simplifies cross-platform graphics application development by providing an internally consistent and cohesive framework that emphasizes platform-independence. Similar in function to Microsoft's Windows Presentation Foundation (formerly called Avalon) and Apple's Quartz 2D, Cairo has been widely adopted within the open source community and is currently used in numerous open source applications and frameworks including the GTK toolkit and GNOME desktop environment.

Firefox uses Thebes, a C++ wrapper for Cairo. It is hoped that incorporating Cairo into Firefox will decrease the amount of graphics code that needs to be maintained by the Firefox developers, simplifying the Firefox code base and making it easier to further improve Gecko rendering. Cairo opens the door for hardware-accelerated rendering in Firefox using Glitz, Quartz, or an accelerated X server like Xgl. Cairo will also eliminate some awkward rendering bugs, provide new drawing functionality, increase the general quality of anti-aliasing, and improve native SVG support.

SVG improvements in Gran Paradiso are already evident. In a recent message posted on the Tango artists mailing list, Tango contributor and Mozilla Visual Identity team member Steven Garrity provides a nice comparison to show how the SVG improvements in Firefox 3 affect the rendering of SVG Tango icons.

SVG icon comparison courtesy of Steven Garrity

Although Cairo has a lot to offer, the library itself still has some deficiencies. It is under heavy active development and has improved considerably, but there are still relatively significant performance issues that have to be resolved. Recent benchmarks conducted by Zack Rusin reveal that Cairo is quite a bit slower than Qt 4 in some contexts. A new Bently-Ottman tessellator being developed by Carl Worth and others on the Cairo team could potentially resolve a number of Cairo's performance problems.

There are some new bugs in Gecko 1.9, some of which have been introduced into Gecko as a result of the move to Cairo. An assortment of minor font rendering issues have been documented in Gran Paradiso on all three major platforms and compatibility issues have been reported by Linux users who aren't running at least Xorg 7.

Gran Paradiso alpha builds for Windows, OS X, and Linux are available for download from the Firefox FTP as well as the source, but it is important to note that these early alphas are experimental and not intended for regular use. Web developers can use the Gran Paradiso alpha to help ensure that their sites will render properly in Firefox 3, and members of the Mozilla community can use the alpha to help test and debug Firefox. The compressed BZ2 archive containing the Gran Paradiso Alpha 1 binaries and associated files for Linux is about 8 MB, but it expands to about 25 MB after decompression. Before testing Gran Paradiso, you will probably want to back up your Firefox settings directory (~/.mozilla on Linux) so that your configuration data isn't damaged. Those of you that want to test the new reflow improvements can try the latest nightly build, available for download from the Mozilla FTP server. The nightly build, referred to as Minefield, is extremely experimental.