Firefox Color is amazing extension by Mozilla that provides simple yet powerful GUI to create custom Firefox themes. It is unfortunate that it hasn't been updated for 4 years, which steadily increases chances of severe issue appearing. The add-on should be reviewed and updated, at the very least by showing current design in the preview instead of the old one (current one is Proton and the old is Photon, right? anyway, to the topic). Other possible improvements may include:
* built-in gradient support for backgrounds
* better description of what each color class do
* mobile Firefox support
* Thunderbird support (see https://connect.mozilla.org/t5/ideas/merge-thunderbird-add-ons-website-with-addons-mozilla-org/idi-p... for details on Thunderbird add-ons website)
* light/dark variants for a single theme
* system colors support.
The core of this Idea is, however, is to bring back some attention to Firefox Color and not let it die, since it's not just cool or useful – it enables all user to create and publish custom themes, unleashing their creativity and giving them ultimate control over how Firefox looks, no matter their experience in UX design.