There are so many websites (and in particular, web applications) where the vendor got a minor thing wrong. With Stylus and a bit of quality time with the Firefox Inspector, many of those issues can be easily papered over. And that's more than cosmetics: a password vault that uses fonts that mix up small L and digit one is a hazard, and an application where a tighter linespacing removes an unnecessary nested scrollbar becomes just a bit more productive. In short, Stylus is ideal whenever you can't just edit the CSS behind an application.

This is great for customizing my read experience on many, including company-internal websites, where I don't like their styling.

It's a great extra but currently the inline style picker isn't working.

Stylish site never loads. Just a spinning color wheel forever. It's not Stylus's fault, but since it's an integral piece of what this add on does, it's just not that useful anymore.

Nice

Очень хорошее расширение. Любой сайт с ним преображается.

Very convenient. Somehow it took me months to figure out how to make a style apply only to the current url (click the url parts in the small popup that opens when clicking the extension). I think the UI could be simplified to make it more user friendly, but overall it's quite good.
Some of my use cases :
- add `body{background:red} ` on your production website to not confuse it with staging.
- hide the advertising line at the top of the mailbox in yandex mail
- make a touch typing website responsive and ad free

I already have an ad blocker but this lets me get that ads space back for content.