[CentOS] Unable to start Firefox/Mozilla after yum updates

Since installing the latest yum updates a couple of days ago, I'm unable 
to start Firefox or Mozilla. Both fail silently with no messages printed 
to console. This is a 32-bit dual Xeon box running Centos 4.2.

Here's what i've tried so far.

- uninstalled and reinstalled firefox and mozilla packages with yum.

- deleted my mozilla preferences (~/.mozilla) in case of a corrupted 
profile.

- running as root. only difference is now mozilla segfaults instead of 
failing silently.

- setting debug options in the firefox and mozilla startup scripts ("set 
-x"). the debug output looks identical to another machine I have on which 
firefox works, so this is no help.

- checked system logs.

Anyone with more knowledge of firefox/moz know what could cause a silent 
failure like this? I can provide debug output if needed, but I didn't see 
anything useful in it. Thanks.

slaton