I've done some research at mozilla and adobe and tests with both recent LTS-versions (14.04 and 12.04) and I'm pretty sure it is just a numbering problem of the flash-plugin!
To make a long story short:
If you open in firefox "tools" - "add-ons" - "plugins" respectively look at the mozilla check and you've got version 11,2,202,425 (notice the commas!), you will get this error message.
and if your version is 18.104.22.1685 (same version, just with dots at the numbering) everything is fine.
So don't panic, your system is safe! ;-)
But I can understand that this message is annoying and so this would be the easiest way to get rid of it:
open a terminal and insert
sudo apt-get update && sudo apt-get install -y flashplugin-installer, type your root-password (no characters will be displayed) and just wait till executed!
I would recommend this solution just in the case you have already installed the latest version but still get the error message because of the differences between the flash-packages!
about:pluginsin your Firefox address bar, and search for flash player. What version does it list? Does it list 22.214.171.1244 or 126.96.36.1994? Go to Adobe's flash version tester (clicking "Activate Adobe Flash"), and look at what version it says you have. Does it say "You have version 11,2,202,424 installed" or "11,2,202,425"? 188.8.131.525 is the proper latest version. For some reason Firefox seems to mis-detect what version is installed. Finally, exactly what version of the flash package do you have installed on your machine?
about:pluginssays 184.108.40.2069; adobe's site says 11,2,202,359 If I install
about:pluginssays 220.127.116.115; adobe's site says 11,2,202,425
adobe-flashplugin). That, combined with the details from DJCrashDummy, sounds like the answer. Want to post an answer that explains all of this? This should be very useful to others.