This problem starts with Firefox reporting that your flash-plugin is out of date.  This report looks like this and disables all flash.

After this we will take a look Mozilla’s Plugin Check to see what it thinks is going on.

Now here we can see that version 11.2.202.440 is vulnerable.  We will then check about:plugins to see if it agrees.

Again this is also reporting 11.2.202.440, so there must be a problem, but it also tells us that there is an update available.  Now I run regular yum updates on this machine, and I actually noticed flash-plugin was updated just a few hours prior to seeing this alert.  So lets check the installed version.

bash 
yum info flash-plugin
Loaded plugins: langpacks, refresh-packagekit
Installed Packages
Name : flash-plugin
Arch : x86_64
Version : 11.2.202.442
Release : release
Size : 19 M
Repo : installed
From repo : adobe-flashplayer
Summary : Adobe Flash Player 11.2
URL : http://www.adobe.com/downloads/
License : Commercial
Description : Adobe Flash Plugin 11.2.202.442
: Fully Supported: Mozilla SeaMonkey 1.0+, Firefox 1.5+, Mozilla
: 1.7.13+

Interesting 11.2.202.442, which is higher than what Firefox is reporting.  Of course Firefox has been rebooted, but lets do it again just to make sure.

Now to fix it.

bash 
pwd
/home/matthew/.mozilla/firefox/cls7wbvm.default
mv pluginreg.dat pluginreg.dat.bak

Restart Firefox and it will collect new data on all of its plugins, and about:plugins will start reporting the correct version.