This bug is the RHEL 4.x clone of bug 460368. It's a ppc/s390 specific issue, inside Firefox sources, tracked by Mozilla upstream http://bugzilla.mozilla.org/show_bug.cgi?id=456945 ONLY for TRACKING. The real fix will get included (hopefully) with an upstream fix, and can be shipped as part of the next future Firefox update (probably 3.0.4).
Upstream is marked as fixed by Firefox 3.0.4, which has been shipped into RHEL 4 long ago, so this should be fixed.