Add Firefox template (userChrome.css / userContent.css) using the Noctalia palette

[venus-fire]

Template

• App: Firefox
• Template id (directory): firefox
• New template

What it themes

Firefox's native userChrome.css / userContent.css mechanism:

• firefox-userChrome.css — tab bar, navigation toolbar, URL bar + results,
  bookmarks bar, sidebar, find bar, menus/panels, context menus, dialogs,
  autocomplete popups, download panel, web select dropdowns.
• firefox-userContent.css — about:newtab/home, about:preferences and its
  sub-dialogs, about:addons, about:logins, about:protections,
  about:config, about:profiles, etc.

Dark and light variants are generated; Firefox switches via prefers-color-scheme.
No extension required (the Pywalfox-based pywalfox/pywalfox-beta4 templates
stay available for the extension path).

Testing

Tested as a user template on this machine (Noctalia v5.0.0), theme applied via
noctalia msg templates-apply.

• App version tested: Firefox 153.0.3 (profile under ~/.config/mozilla/firefox)
• Applied a dark theme and confirmed the app picked it up (screenshots below)
• Applied a light theme and confirmed the app picked it up
• Re-applied twice and the app config is still correct (hooks are idempotent)

Screenshots

Hooks

• What the hook does: finds Firefox profiles by locating prefs.js
  (regular ~/.mozilla/firefox, $XDG_CONFIG_HOME/mozilla/firefox, Flatpak,
  Snap), creates the profile chrome/ dir, adds the Noctalia @import lines to
  userChrome.css/userContent.css, and enables
  toolkit.legacyUserProfileCustomizations.stylesheets,
  svg.context-properties.content.enabled and devtools.chrome.enabled
  through the profile's user.js.
• It is idempotent: running it twice does not duplicate lines or corrupt the config.
• It fails loudly (non-zero exit, message on stderr) when the app's config is missing.
• It downloads nothing and executes nothing it did not ship in this directory.
• It touches only this app's own config.

Checklist

• The directory name matches the [catalog.firefox] id in template.toml.
• category is one of: ai, audio, browser, chat, compositor, editor, gaming, launcher, system, terminal, misc.
• Every input_path names a file that exists in this directory.
• No generated output or app-specific personal config is committed.