Before anyone hit's me over the head with "File a Bug Report" I'll save you the time you didn't take in checking to see if there was a bug and, there is. #505365 to be exact. The work around is known, it's a matter of waiting until Fedora decides on how to fix it.
Meantime, Firefox still crashes. So what to do. Well in dealing with the bug and in dealing with some stack traces I did, we came to the same idea. There are a number of libs in Firefox, that are referenced by Firefox, the same names are referenced by flash. The problem comes when Firefox runs it says "Do I have this lib if so use mine." and Flash says "Use the lib referenced by ldconfig" OOOOOPS!
Yep, you now have conflicting libs, and the end result is a total panic by Firefox, resulting in a crash. The solution? Remove the conflicting libs from the Firefox directory (where Firefox expects them to be) and poof. All is well in surfing land. If Firefox can't find the libs locally it happily uses the system libs without missing a beat.
The procedure is as follows. ($ is used to represent a command prompt)
$ cd /usr/lib/firefox
$ sudo mkdir lib-hold
$ mv libfreebl3.chk libnss3.so libnssutil3.so libsmime3.so libssl3.so libfreebl3.so libnssckbi.so libplc4.so libsoftokn3.chk libnspr4.so libnssdbm3.so libplds4.so libsoftokn3.so lib-hold/
Now just install Flash as you normally would and viola, you now have a working flash installation that doesn't crash Firefox.