How to install Flash on Debian Stretch?

The flashplugin-nonfree package is no longer maintained, if you need the Flash plug-in you should install it manually:

  1. Download the latest release of the plugin in tar.gz format from Adobe.

  2. As root, extract the downloaded archive and copy to /usr/lib/flashplugin-nonfree.

  3. Fix the file’s ownership and permissions:

    chmod 644 /usr/lib/flashplugin-nonfree/
    chown root:root /usr/lib/flashplugin-nonfree/
  4. If necessary, install the alternative so Firefox will find the plug-in. If

    update-alternatives --list

    returns /usr/lib/flashplugin-nonfree/, it’s set up correctly (this would be the case if you had the plug-in working in the past), but if it doesn’t, you need to run

    update-alternatives --quiet --install /usr/lib/mozilla/plugins/ /usr/lib/flashplugin-nonfree/ 50

For future upgrades, you only need to repeat the first three steps.

Alternatively, pepperflashplugin-nonfree still works and will install the Flash plug-in for Chromium. You’ll need to download the package manually and install it using dpkg -i, but it will download the plug-in and set everything up for you. You can keep the plug-in up-to-date by running update-pepperflashplugin-nonfree --install (and check its status using --status).