“Firefox 1.5.0.2 provides native support for Macintosh with Intel Core processors, and stability and security enhancements that are part of our ongoing program to provide a safer Internet experience for our users. We recommend that all Firefox users upgrade to this latest version.”
Mozilla
some links added
Undoclosetab, one of my most-used extensions, stopped working with this update, but a simple tweak from the mozillaZine forum made it work.