Crayon: custom CSS injector — Morgân von Brylân

A fork of CustomCSS Injector by Blizz3.
Like CustomCSS Injector, it lets you write CSS rules to be applied to any website. Anything CSS can do, this can do.
Rules can be set globally, for a given domain, or for a specific URL.
Write them in the built-in editor with syntax highlighting (thanks to PrismJS) in the pop-up and hit "Save". No page refresh required!

On top of that, Crayon also provides the following features that (at the time of writing) Blizz3's add-on doesn't:
– Combine global, domain and URL rules: if several rulesets could apply do a page, all of them do, applied in that order (they used to be mutually exclusive).
– An overview page that lets you see all the rules you have set, as well as export/import them.