Adobe Flash Plugin is vulnerable/outdated in 14.04 but there is no update in Firefox

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 11.2.202.425 (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!

The best solution to the problem of a vulnerable, out-of-date Flash installation--or even an up-to-date one that works poorly--may be to uninstall Flash entirely. Often it is not needed, as HTML5 has largely taken over. Thus removing Flash is a real solution for many people, and should probably be considered first before moving on to other solutions that attempt to keep Flash installed while maintaining it in a current (or semi-current) state.

As occupyflash.org says:

Flash Player is dead. Its time has passed. It's buggy. It crashes a lot. It requires constant security updates. It doesn't work on most mobile devices. It's a fossil, left over from the era of closed standards and unilateral corporate control of web technology. Websites that rely on Flash present a completely inconsistent (and often unusable) experience for fast-growing percentage of the users who don't use a desktop browser. It introduces some scary security and privacy issues by way of Flash cookies.

Flash makes the web less accessible. At this point, it's holding back the web.

Following solution worked for me:

sudo apt-get purge flashplugin-installer
sudo apt-get install adobe-flashplugin