Get it here:
Windows: http://download.mozilla.org/?product=firefox-1.5&os=win&lang=en-US
Mac OS X: http://download.mozilla.org/?product=firefox-1.5&os=osx&lang=en-US
Linux: http://download.mozilla.org/?product=firefox-1.5&os=linux&lang=en-US
*installed, this feels much snappier than 1.07. hmm!