基本的には良いんですがFirefoxだけこの拡張機能有効にしてると少しパフォーマンスが落ちます
Chromeはパフォーマンスに影響しないのですが。。。

Need to be able to easily make rules for sites. For example, I can't set it to use a theme globally but then disable that theme and/or use another one on specific sites. I've yet to find a theme that looks good everywhere, so the ability to customize per domain, and even per page, is a necessity.

UI is very poor in Firefox Quantum

Does not work on Firefox 56 for Android.

I am getting "This add-on requires a newer version of Firefox (at least version 55.0). You are using Firefox 52.0." But I am actually using Firefox 57.0! What sorcery is this?

Edit:

I downloaded version 1.1.4.2 of Stylus and was then able to update to version 1.5 from Firefox's add-on manager. Stylus add-on page still says my version of Firefox is 52.0, though.

it can't work in Firefox mobile 57

I can't find the preview button!
Do i have to save it to test it?

I'm using FF beta channel (56b11), it says "in this version of Firefox: chrome.extension.getBackgroundPage() doesn't return a valid result", which makes it unuseable.

No options to import scripts or install via Stylus when browsing to a script on userstyles.