Netscape 7.1 is based on a now ancient version of Mozilla (1.1? Something like that). NS also has nasty AOL-ifyied extra bits bolted on.
Firefox is a cut-down version of the Mozilla browser component, and they still share source code.
There's also Thunderbird, the standalone email client, currently at v0.5, which is also quite nice. I've been using it since 0.4 was released.
Mozilla on AmigaOS/compatibles would be a much-needed boost to Amiga opensource development, not to mention great PR, as well as giving me a decent footing for migrating to OS4 :-)