https://www.reddit.com/r/chrome/comments/1ymfgw/user_stylesh...
(The comment there that removing this "is going to help increase speed significantly in the future" is pure BS. If anything, user stylesheet functionality was handled in native code --- just adding another CSS to the page --- which makes it far more efficient than going through the whole JS/extensions route.)
Ironically, IE11 is the last MS browser to support user stylesheets (Tools->Options->Accessibility) but Edge doesn't.
Even in Firefox, the fact that it's named "toolkit.legacyUserProfileCustomizations.stylesheets" is ominous.
The Internet is becoming more and more user-hostile, and it's not just websites who are responsible.