Seamonkey
ftp://ftp.mozilla.org/pub/mozilla.org/seamonkey/releases/1.0.4/contrib/
Firefox
http://ftp.mozilla.org/pub/mozilla.org/firefox/releases/1.5.0.6/contrib/
SeaMonkey is a continuation of the Mozilla Suite, which was discontinued by the Mozilla Foundation. Firefox is a stand-alone browser, based on Mozilla code.
Note that current builds require an updated version of ipluginw.dll for Java support; see my Warpzilla tips page for more information.
http://www.os2bbs.com/os2news/Warpzilla.html
In semi-related news, you can see current plans for the Mozilla branches. Thanks to Gary Wong for the info.
http://wiki.mozilla.org/Global:1.9_Trunk_1.8_Branch_Plan
Source: OS/2 Warp News and Rumors