The first beta of FireFox 1.5 is now available for those folks who wish to give it a spin. This release is aimed more at testers, extension/theme authors and web developers than standard users at this point so you may want to hold off for the final release due later this year if you’re not one of those folks.
Firefox 1.5 Beta 1 can be downloaded from the Firefox project page or the Firefox 1.5b1 directory on ftp.mozilla.org. The Mozilla Firefox 1.5 Beta 1 Release Notes have more information and The Burning Edge has an unofficial list of what’s new in Firefox 1.5 Beta 1.
Sounds like the final release will be worth the wait.