The irony is that I ported two of my old user scripts to web extensions. With old Opera, userJS was native, while TamperMonky is a (big) web extension. I had pe

The irony is that I ported two of my old user scripts to web extensions. With old Opera, userJS was native, while TamperMonky is a (big) web extension. I had performance problems with TamperMonkey, so I rewrote my scripts to avoid this layer. Pros of TamperMonkey/userJS: - Allows live editing (with syntax highlighting) with immediate refresh, all in the browser. This is handy for minor changes on small files, but slow for big files. - Direct access to some HTML5 APIs that are restricted in extensions. I don't recall if that was the case with TamperMonkey, but OperaJS allowed plain AJAX and WebStorage usage, just as if the file was included in the web page. Cons: - Slower than extensions. - Less powerful (cannot add a button in a browser bar, etc) - Painful as code grows. An extension allows simple splitting of code into several files. I found UserJS harder to maintain. - Cannot load JS _and CSS_ like an extension does. Another extension like Stylus is needed.