userChrome Toggle
userChrome Companion
This is userChrome Companion. Instead of relying on the about:config page and user.js, I see a future where FF Ultima could work alongside userChrome Companion. Depending on the development of`UCC and how much easier it is for both you and me, it can become a possibility.
UserChrome-Toggle extension support
userChrome toggle allows you to switch between styles through a simple button-click or even a keyboard-shortcut. If you have more creative ways of using this extension and want to see it implemented into the theme, feel free to pull request or create an issue. We'll see if it can be done.
The theme used to integrate userchrome toggle with a vertical tabs shortcut, but this feature has been mainstreamed to Firefox via the new Sidebar button (since version 131). If anyone would like to see the userchrome toggle extension used in different ways, feel free to PR an implementation.