flashplugin-nonfree software package provides Adobe Flash Player - browser plugin, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install flashplugin-nonfree
flashplugin-nonfree is installed in your system.
Make ensure the flashplugin-nonfree package were installed using the commands given below,
$ sudo dpkg-query -l | grep flashplugin-nonfree *
You will get with flashplugin-nonfree package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Web Software |
| Package | flashplugin-nonfree |
| Version | 01:03.70 |
| Description | Adobe Flash Player - browser plugin |
| Sub Section | Web |