The basis of the Web is interoperability. Five browser vendors are involved in the standardisation of HTML5: Opera, Mozilla/Firefox, Microsoft/IE, Apple/Safari, and Google/Chrome. With the development of HTML5 and the large amount of new features that are being introduced, interoperability is not always a given. Not only do browsers implement new features at different speeds, they also disagree on what functionalities should be implemented, and frequently fail at interpreting the specification in the same way. The opportunity of HTML5 is innovation, so we want browsers to implement and show off new features. But at the same time we want them to be solid and usable and, above all, interoperable. So, how do we solve the dichotomy between progress and interoperability?