Pop OS is a great Linux distribution for desktop which is based on Ubuntu 17.10 Artful Aardvark. Pop OS is developed by System76, a laptop/desktop manufacturer who ships Linux on their products. Pop OS is a great Operating System but unfortunately it does not have flash plugin or flash player installed by default. In this case, you won’t be able to play videos in your Facebook when using Firefox.
You may check if Flash Plugin is available by typing the following address on Firefox:
As you can see, only one plugin is available.
But this issue can be fixed very easy. We can install Pepper flash plugin on Pop OS with the following command
sudo apt install browser-plugin-freshplayer-pepperflash pepperflashplugin-nonfree
Now restart Mozilla Firefox and check if flash plugin is correctly installed.