Thank you!

very nice and fast

I modify font-family with Stylus.
I cannot live without this addon.

It used to work great but the functionality to search for existing themes for the site you're on takes a very long time to search, and for some sites just doesn't ever return any results.

Slow or unresponsive. It's a waste of time to even try to get it working

Cette extension est fantastique, exactement ce que je cherchais.

Great addon! It has made me happy for years. But now I have to migrate all my styles to Tampermonkey scripts due to the following reasons:
1. Firefox (both Windows and Android) cannot work normally with userstyles.org: lags all the time, almost impossible to edit styles on this web-site. These problems last for more than a month and I'm tired fighting them.
2. This addon works only partially in new Firefox for Android and Firefox Nightly: it applies styles well, but cannot edit them locally and cannot update them with new version from userstyles.org.

I will keep an eye on it. Maybe I'll be back later :)