Netscape uses its own threading model, and provides an override for the select() function call to prevent a rogue thread from blocking the whole process. Unfortunately, it fails to provide a similar wrapper for the poll() function call, with the disastrous effect that any library or plugin using poll() will cause netscape to lock up. The category of 'library or plugin using poll()' happens to include the latest version of the XFree86 libXt. This is, to say the least, unfortunate. It's fairly likely that there's already a netscape wrapper for poll(), used on some other *nix platform, and that it just needs to be enabled for compilation on the Linux build. Even if not, it should be trivial for someone with access to the Netscape source to provide one, and possibly distribute it as an LD_PRELOADable library, if not an updated binary. I'm not sure if Red Hat has access to the Netscape source tree in order to maintain the "linux2.2" (actually more accurately named "glibc2.1") version of the browser, but even if not, it might be possible for Red Hat to ask Netscape to produce this modification/library. If Red Hat doesn't have Netscape source access - then perhaps it could be arranged. I'm fairly sure that Netscape do provide source to platform vendors in order for them to maintain specific versions of the browser. Red Hat could do the same.
It's known about and reported to netscape; no fix yet aside from compiling the latest Xt without poll() support.