Firefox 1.5 was released yesterday.  Read about why this is a significant upgrade in the release notes.

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Coolest features:

• Auto-update - you can now keep firefox up to date without downloading the whole new version
• Drag & Drop re-order of tabs - I've been waiting for this for a long time
• Native SVG support (the inkscape fans cheer)

The really cool stuff (like SVG) is under the hood: 

Based on the Gecko 1.8 engine, this newest version of the browser improves its already best in class standards support, and provides new capabilities to enable the next generation of web applications. Firefox 1.5 features improved support for CSS2 and CSS3, APIs for scriptable and programmable 2D graphics through SVG 1.1 and <canvas>, XForms and XML events, as well as many DHTML, JavaScript, and DOM enhancements.

See:   http://developer.mozilla.org/en/docs/Firefox_1.5_Beta_for_Developers