The attributes got renamed in PR #126440 and in some places this caused
evaluation errors, e.g. the tarball job was saying (locally)
> attribute 'alsaUtils' missing, at /build/source/nixos/modules/services/audio/alsa.nix:6:4
and I suspect that trunk-combined jobset's failure to evaluate was also caused.
Run Firefox inside an XTerm, it doesn't crash mysteriously this way.
Also try opening developer tools and checking that Firefox doesn't
crash in the process.
You can now run a test in the nixos/tests directory directly using
nix-build, e.g.
$ nix-build '<nixos/tests/login.nix>' -A test
This gets rid of having to add the test to nixos/tests/default.nix.
(Of course, you still need to add it to nixos/release.nix if you want
Hydra to run the test.)