Mozilla Firefox 1.5 Beta 1 is now available for download. This is the first beta release of the next major Firefox, which will be widely promoted to end-users, is scheduled for later this year.
New features include an improved software update system, faster Back and Forward navigation (I’m testing it and it’s really fast!), a feature for clearing private browsing data, drag-and-drop reordering of browser tabs, a redesigned Options/Preferences window and better popup blocking. Web standards support is also improved:

• Support for Scalable Vector Graphics (SVG)
• JavaScript 1.6 and more CSS
• Accessibility is also better (including new DHTML accessibility features)
• Security has been enhanced and there’s now greater support for Mac OSX

Please note that installing FireFox over previous version will disable almost all downloaded extensions which are not compatible with this version of Firefox.
Beta 2 is scheduled for release on Wednesday 5th October and the first release candidate is due on Friday 28th October.
http://www.mozilla.org/projects/firefox/