You're getting your browser history mixed up a little -- Phoenix was a reaction against the general bloat of Mozilla, but it was still a cross-platform XUL-based affair.
"Phoenix is a redesign of the Mozilla browser component, similar to Galeon, K-Meleon and Chimera, but written using the XUL user interface language and designed to be cross-platform."
Check out the Phoenix 0.1 announcement: http://website-archive.mozilla.org/www.mozilla.org/firefox_r...
"Phoenix is a redesign of the Mozilla browser component, similar to Galeon, K-Meleon and Chimera, but written using the XUL user interface language and designed to be cross-platform."