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According to the release notes, the core Gecko rendering engine--the component that interprets Web page instructions and draws text and graphics on your screen--has seen major changes in the upgrade to the new version 1.9 used in Firefox 3. "Gecko 1.9 includes some major re-architecting for performance, stability, correctness, and code simplification and sustainability," the notes said. Those changes "put foundations in place for major performance tuning which have resulted in speed increases in beta 1, and will show further gains in future beta releases."