404 for the full changelog :/

Auch fragt man sich, ob es Absicht ist, dass im Nebensatz nicht der Konjunktiv bemüht wurde …

If using flakes you could just for instance add another input. You can also set the input URLs to specific states of the nixpkgs repository by eg referencing specific commits. Then, you should be able to just, e.g., pick Firefox from unstable, another package from the current stable channel, and maybe a broken package from a pull request fixing said package.

If you are not using flakes you can also add system wide channels. IIRC you can then import these channels into your configuration.nix and select packages from the corresponding channels. But here the channels/inputs are not part of configuration itself in contrast to when using flakes.

This procedure doesn't work with flakes as they come with "channels included".

If you are using flakes you should check your flakes' inputs (probably the one called nixpkgs) and then change the URL to match the channel for 23.11. Finally, you should of course rebuild your system.

You could choose any extension from the extension store

You can still more or less do this if you create an add-on collection and add all your extension to it. In order to register this collection with Firefox you then have to enable the Debug Mode by clicking the firefox logo in firefox's about section 5 times.

It may be possible that you need Firefox Beta or Fennec for this to work

Ich bin mir nicht sicher, ob es der Debatte zuträglich ist so plumbe Argumente zu teilen. Konnte allerdings nur die ersten 1.5 Absätze lesen, da Paywall.