It looks that essential "Requires: xulrunner" (for RHEL <=5) " or Requires mozilla-filesystem" (RHEL >=6) was escaping to our spec files for eons. This package is creating this directory. It was just luck that it was bring by some transitive dependence. Simple adding of those packages as dependence for plugin should solve this problem.
*** Bug 795358 has been marked as a duplicate of this bug. ***
This was found as bug in xulrunner after reabase to 10. Reasigning to proper component and owener.
*** Bug 800137 has been marked as a duplicate of this bug. ***
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. http://rhn.redhat.com/errata/RHSA-2012-0387.html