Save the file to your desktop.
Now open a terminal and enter the code in bold below:
This will make a folder in Mozilla Firefox's directory called plugins. This is were we will be moving the file we downloaded.
We just need to change the terminal current directory so it can find the we downloaded. using cd will tell the terminal to chage directory and entering the directory path after cd will show the terminal the new directory. This can be seen in the code in boldbelow, enter this into the terminal.
Now we will move the file using the code in bold below. Just enter this into the terminal and the file will move itself to the correct place.
mv -f libflashplayer.so ~/.mozilla/plugins/
To check this work go to youtube in Mozilla Firefox and try place one of the videos.
(note: dont forget to disable Mozilla Firefox addon NoScript because it blocks flash applications)
If that worked then your all done!