TLDR: popularize Firefox uC styles among regular users by representing them as content downloadable from AMO (just like regular themes) and promoting this 'advanced customization' as a unique feature and not something shady used only by "power users".
One of the greatest advantages of Firefox over other browsers is its interface is highly and easily customizable, thanks to using XUL for its UI. With minimal knowledge of CSS and 1-2 hours of learning you can change almost anything you want!
Firefox GNOME Theme One of a few dozens one-liner styles FlyingFox MaterialFox
Knowing that, it's weird to see Mozilla doesn't do anything about this feature at all! For example, to install the style, you have to enable uC support (labeled as "legacy stylesheets") in advanced settings which regular users won't ever go to, then find a style on potentially unsafe community forums, and then manually "install" it by moving it to the chrome folder. Not to mention this feature seems to never was actively developed, not allowing to anyhow store several styles, having several security vulnerabilities etc.
So, what do I think Mozilla should do:
Actively promote this feature as one of Firefox's benefits (because it is). Most Chromium-based browsers can only provide a very limited customization options, so Firefox will definitely stand out with this. Most of them don't even allow you to rearrange toolbar icons! For example, take a look at Vivaldi - one of its selling features is high (comparing to other Chromium-powered browsers) customization, and Firefox can potentially provide way more options!
Improve the way userChrome works now The idea is to treat uC style the same as regular extensions and themes, providing config keys as extension permissions. This also means it'll require to ensure the uC style security (make a verification to protect browser from malicious sideload, fix possible security vulnerabilities (e.g. allow uC styles to load only other CSS files and PNG/SVG images) etc.) and maybe document some unclear parts of it somewhere on MDN.
Create a section for userChrome styles on addons.mozilla.org AMO Styles page mockup with a few themes showcased.Since the sideload will no longer be an easy option (though still possible for debugging), people obviously would need a place where they can easily download uC styles they want. Why not provide them with one then? They also should be clearly distinguished from themes, as the first ones intended for simpler customization and most of uC styles are fully theme-compatible.
What do you think? Hope this suggestion will get some good feedback 🙂
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