The only addon that gives the complete "Before-57" experience, and even more! I was able to convert the broken Stylish.sqlite database, and import all my 70+ hand-made styles. Everything works as intended. Thank you!
What about these two features: 1) customizing browser-specific pages (like about:home, context menus) or addon pages (w/o userChrome.css); 2) using the external editor to edit CSS (Notepad2, Notepad++, Brackets)?
Is it the matter of time, or these features won't be ever available with the Web Extensions API?
WebExtensions API cannot apply CSS to built-in pages or browser UI. See the Mozilla roadmap: https://wiki.mozilla.org/WebExtensions/RoadMapFirefox57#Theming - they're working on a limited Theming API, which is not CSS-based hence useless in Stylus, but other extensions will definitely appear that utilize it.
