2. Let the Package installer software install it. Restart firefox and it should be working.
If it’s still not working, follow the following steps.
3. Open Terminal and input
$> firefox &
to execute firefox.
4. Go to youtube.com and click on any video. It will be just like step 1 but this time you can see the error message from the Terminal. For me, the error messages say
LoadPlugin: failed to initialize shared library /usr/lib/adobe-flashplugin/libflashplayer.so [libnss3.so: cannot open shared object file: No such file or directory]
The problem is not in flash player but because of a dependency lib of flash player mssing .
5. Open Synaptic package manager (System >> Administration >> Synaptic package manager) and install the missing lib (libnss3). Restart firefox and the flash should work fine.