Description of problem:
After upgrading Firefox from version 3 from F14 to version 4 from F15, Firefox started to crash immediately on startup.

Version-Release number of selected component (if applicable):
selinux-policy-targeted-3.9.16-26.fc15.noarch
firefox-4.0.1-2.fc15.x86_64
xulrunner-2.0.1-1.fc15.x86_64

How reproducible:
Every time

Steps to Reproduce:
1. setsebool allow_execmem=off allow_execstack=off
2. firefox
  
Actual results:
Firefox crashes and a crash report window comes up.

Expected results:
Firefox should run.

Additional info:
After some investigation and some helpful comments on the fedora-selinux mailing list (http://lists.fedoraproject.org/pipermail/selinux/2011-June/013837.html) I figured out, as shown above, that disabling both allow_execmem and allow_execstack is necessary to trigger the problem.  These are not the default settings, so in a standard configuration this won't happen.  But I was under the impression the intention was it should be possible to run a system with these booleans turned off.

Dominick Grift suggested in the mailing list thread to make the Firefox binary "execmem_exec_t".  By default it has the type mozilla_exec_t.  I'm not sure in what way that is different from bin_t, but I assume there is some difference. So maybe the "proper" fix is to add transitions to the policy based on that type instead.

From what I can understand, it would make sense for the policy to allow the firefox binary to do execmem.