There's some more work to do to build on bug 1762817 to get presets fully operational. An example preset I was experimenting with was dom.toml but I didn't end up shipping that. The main limitation was that in chew_query.rs I just copped out and used lazy_static to incorporate
query_core.toml rather than doing the filesystem legwork required. I've since enhanced the config mechanism with read_tree_config_file_with_default and maybe_read_file_from_given_root which could probably grow a method that would happily wildcard a given config directory sub-dir (and allowing for other m-c trees to just point at mozilla-central) to provide a bunch of paths to consume.