First go to download directory Flash Download
If drop down does not specifically state a Ubuntu with you version then download the newest Linux version available with extension “gz”.
locate the FireFox directory where plug-ins are located. Simplest way to do this is just search for an existing plug-in. Go to Add-ins then on right select plug-ins then choose on and click more. That gives you the name of it’s file. Take that file and do a search for it.
For me it was located at usr/lib/mozilla/plugins
unzip the download and move the “libflashplayer.so” to the plugin dir.
sudo cp /home/ceb/flashinstall/libflashplayer.so libflashplayer.so
then from the directory where you unzipped the plug-in run the following
sudo cp -r usr/* /usr
Now if you go to plug-ins again inside Firefox you’ll see your new plug-in ready to go