Test against FF ESR and see if reasonable target to support

[nexushoratio]

It could be that nothing would work anyway, US manager wise.

ESR between Debian Bookworm and Mozilla downloads are similar: 140.{10,11}

Sidenote: Current Debian LTS (11/Bullseye) is aging out soon (2025-08-31), so no need to investigate it.

[nexushoratio]

Initial testing with VM and LIT seem promising, so add it to the support matrix.