At least for EL5 users, Red Hat's update today looks like it may solve what's happening in this thread.
https://rhn.redhat.com/errata/RHBA-2012-1429.html
* The "out-of-process plug-ins" feature was previously disabled for wrapped
plug-ins by default. This could cause Firefox to terminate unexpectedly when
accessing a page that contained a flash object and the flash plug-in and the
nswrapperplugin plug-in viewer were installed. To resolve this problem, the
"out-of-process plug-ins" feature has been enabled for the wrapped plug-ins.
Firefox no longer crashes in this scenario. (BZ#871568)