Installing

There are two parts: the helper, which reads caelestia’s files, and the extension, which the browser runs. The extension works without the helper, but then it has no scheme or wallpaper and falls back to a fixed dark red.

The helper

With Nix:

nix profile install git+https://git.hu-tao.dev/hutao/caelestia-tab
caelestia-tab install

With Cargo:

cargo install --git https://git.hu-tao.dev/hutao/caelestia-tab
caelestia-tab install

caelestia-tab install writes the native messaging manifest, caelestia_tab.json, to ~/.mozilla/native-messaging-hosts/. It also writes it to the matching directory of every fork whose home directory exists (~/.zen, ~/.librewolf, ~/.floorp, ~/.waterfox). The manifest holds the helper’s absolute path, so run install again if the binary moves. caelestia-tab uninstall removes the manifests.

On NixOS or Home Manager

A path in the Nix store changes on every update, so it’s better to let the browser wrapper link the manifest than to run install. The package ships the manifest in lib/mozilla/native-messaging-hosts/, the shape nixpkgs’ Firefox wrapper expects:

home.packages = [
  (pkgs.floorp-bin.override {
    nativeMessagingHosts = [ inputs.caelestia-tab.packages.${pkgs.system}.default ];
  })
];

The same override works on firefox, firefox-bin, librewolf and the other wrapped Firefox packages.

The extension

It isn’t on addons.mozilla.org yet. Until it is:

• To try it, open about:debugging, choose This Firefox (or This Floorp, and so on), then Load Temporary Add-on…, and pick extension/dist/manifest.json. It stays until the browser restarts. Build it first: npm ci --prefix extension && npm run --prefix extension build.
• To keep it, build an .xpi with web-ext build --source-dir extension/dist and install it from about:addons (the gear, then Install Add-on From File…). Release Firefox refuses unsigned add-ons. Developer Edition, Nightly, ESR and unbranded builds accept them once xpinstall.signatures.required is false in about:config. Whether a fork honours that preference depends on how it was built; see Browsers.

Zen

Zen’s window needs one more step, a script in Zen’s install directory; see Zen’s window.

Site themes

Firefox asks for “Access your data for all websites” separately in Manifest V3. Grant it in the new tab under Settings, Websites, Allow, or in about:addons, caelestia-tab, Permissions. Without it the new tab still works, but no page gets themed.