Install Flash Player for Watching Video in Ubuntu 16.04 Xenial Xerus (LTS)

Install Flash Player for Watching Video in Ubuntu 16.04 Xenial Xerus (LTS), Ubuntu 15.10 wily werewolf, Ubuntu 15.04 vivid Vervet, ubuntu 14.10 Utopic Unicorn, Ubuntu 14.04 Trusty Tahr (LTS) and Other Ubuntu Derivative System

Adobe® Flash® Player is a lightweight browser plug-in and rich Internet application runtime that delivers consistent and engaging user experiences, stunning audio/video playback, and exciting gameplay.

Installed on more than 1.3 billion systems, Flash Player is the standard for delivering high-impact, rich Web content

Before Install Flash Plugin :

Install Flash Plugin :

sudo apt-get install flashplugin-installer

After Install Flash Plugin :

If, this trick not work :

Please ensure that you have latest version of Mozilla Firefox running.
There are multiple ways to get Flash plugin installed on Firefox.

1. You can go to Software Centre > search for Flash > select the second entry on the page which is 64 bit Flash version. 
2. Go to Youtube in Firefox and run any video. It will prompt you to Install missing plug-in since you do not yet have Flash plugin installed. Click the prompt and follow its process to enable Flash in Firefox.
3. Go to terminal and run this command. It will fetch Flash and other miscellaneous plug-ins for Ubuntu.

 Open terminal and follow the command :

sudo apt-get install ubuntu-restricted-extras

Enjoy! I hope this article adding you more clarity.