SeaOwl for Firefox

A focused userChrome.css that repaints Firefox's chrome — tab strip, URL bar, sidebar, find bar — in the SeaOwl dark palette. Active tab gets a brand-cyan underline, the URL bar picks up a cyan ring on focus, and hover/selection states use the el-hover / el-selected slots. No overrides to page content, no icon re-tinting beyond what the chrome needs, and it never touches your extensions.

1. Open about:profiles and click "Open Folder" next to your current profile's Root Directory.
2. Create a chrome/ subdirectory inside the profile folder if it doesn't exist.
3. Back up any existing userChrome.css, then drop this file in as chrome/userChrome.css.
4. Open about:config and set toolkit.legacyUserProfileCustomizations.stylesheets to true.
5. Restart Firefox.

/seaowl-firefox/userChrome.css