There seems to be some incompatibility between ubuntu and flash releases . I never liked flash player because it tuns very inefficiently on linux but anyways if you have the vulnerability warning ,
do this :
1 ) Get the tar bundle from http://get.adobe.com/flashplayer/
2 ) tar -xvzf install_flash_player_11_linux.i386.tar.gz
3 ) sudo cp libflashplayer.so /usr/lib/mozilla/plugins/
4 ) Restart firefox
Its trivial and irritating .. but this solves the problem..