This isn't new, I remember Opera (versions 12 and older) used to come with a privileged .js file that would apply patches to websites. It was used mostly to fix

This isn't new, I remember Opera (versions 12 and older) used to come with a privileged .js file that would apply patches to websites. It was used mostly to fix those that blocked Opera when they detected its user agent or popular websites that ran code using proprietary functions or css properties (things that only Chrome or Internet Explorer implemented but weren't part of the standard).