Tails

Synaptic now uses software-properties-gtk for managing apt sources (the other parts of Synaptic remained the same).

See the attached screenshots for the workflow. Basically it is:

• Make sure that you are connected to the Internet.
• Start Synaptic package manager.

Changed steps:

• Choose Settings ▸ Repositories.
• In the “Software & Updates” dialog, click on the tab “Other Software”.
• Click on the button “Add…”.
• Copy & paste the following to the field “APT line”: deb http://ftp.de.debian.org/debian/ jessie-backports main
• Confirm by clicking on “Add Source”.
• Click on the button “Close”.

Now it’s the same procedure as it’s in Jessie:

• In the confirmation dialog, click Reload and wait for the download of the package information to finish.
• etc…

The remaining steps are the same as before, this is also the case for everything that is done with the Tails Installer.
I’m not (yet) familiar with the organization of the backports repository, so far it’s needed to use “jessie-backports” (I don’t know when tails-installer will be in stretch-backports, neither when the repo will be available itself).