The Mozilla project is using more and more code that does not compile
correctly with GCC 3.3.x, and they are starting to reject patches that
make it work with the outdated (buggy) compiler. This makes it much
harder to maintain the OS/2 port, and thus efforts were made to get GCC
3.4.x ported to OS/2. The initial fruits of this effort are now
available (9/20/2008) as GCC 3.4.6 from Paul Smedley. You can follow the problems building Mozilla with this version in this Bugzilla bug.
Source: OS/2 Warp News and Rumors.