Description of problem:
Firefox fails to start.

Version-Release number of selected component (if applicable):
firefox-22.0-1.fc19.i686

How reproducible:
always

Steps to Reproduce:
1. Upgrade from F18 to F19 on an ancient Pentium 4 system using fedup.
2. Change the session manager so you can log into a graphical session (bug 955779).
3. Log into an LXDE session.
4. Try to start firefox.

Actual results:
No firefox window opens.  If you watch "ps -ef | grep firefox" quickly, you will see something like
fred     19222     1 65 15:00 ?        00:00:09 /usr/lib/firefox/firefox
fred     19350 19222  0 15:00 ?        00:00:00 /usr/lib/firefox/firefox
quickly followed by
fred     19222     1 63 15:00 ?        00:00:09 /usr/lib/firefox/firefox
fred     19350 19222  7 15:00 ?        00:00:00 [firefox] <defunct>

Firefox will try to start more children, but they will all end up <defunct> and then disappear.

Expected results:
A usable browser window.

Additional info:

Starting firefox from a terminal window shows the following repeated error:
[fred@xxx ~]$ firefox

(process:20199): GLib-CRITICAL **: g_slice_set_config: assertion `sys_page_size == 0' failed

(process:20199): GLib-CRITICAL **: g_slice_set_config: assertion `sys_page_size == 0' failed
...