Distribute as official extension

Firefox Color allows themes creators to easily export their theme as an extension and distribute them in the [Firefox Add-ons Marketplace](https://addons.mozilla.org): <img width="400" height="224" alt="Image" src="https://github.com/user-attachments/assets/035d68df-0efd-4bc4-ab11-b37aa45f4bf1" /> One big issue with the Firefox Color extension is that the default theme will be temporarily flashed during the browser startup, which I find really ugly and jarring. By exporting the theme as an extension, this problem can be entirely avoided. So an official extension distributed by catppuccin org would be really awesome here!