It's literally just a manifest file. In Chrome, you can do it in the Search Engines area, but for some reason it has to be an add-on in FireFox. If someone wants to take it and run with it, I have zero problem with that, TBH. I just posted it since I wrote it for my own convenience in FireFox.

This is the "code" (which is 90% about hello, I am an add-on!).

{

    "manifest_version": 2,
    "name": "Lemmy.ML Community By New",
    "version": "1.0.1",

    "description": "Sorts the searched-for lemmy community by new. So 'c printsf' will return the printsf community already ordered by newest items first.",

    "icons": {
        "48": "icons/icon-48.png"
    },

    "chrome_settings_overrides": {
        "search_provider": {
            "name": "Lemmy Community By New",
            "search_url": "https://lemmy.ml/c/{searchTerms}?sort=New",
            "keyword": "c",
            "favicon_url": "https://lemmy.ml/pictrs/image/fa6d9660-4f1f-4e90-ac73-b897216db6f3.png"
        }
    }

}