Abstract: With the advent of Web 2.0 application, and the increasing number of browsers and platforms on which the Web applications can be executed, XBI (cross browser incompatibilities) is becoming a serious problem for organizations to develop Web based software with good user experience. Although some techniques and tools have been proposed to identify XBI, they cannot assure the same execution when Web application is rendered in different platforms as only user interactions events are considered, which may result in generating both false positives and false negatives. To address this limitation, by leveraging existing record/replay technique, this paper develops X-CHECK, a novel cross browser incompatibilities testing approach and tool, which can faithfully reproduce a previous execution and facilitate XBI detection by directly replaying the captured event trace in different platforms. The same execution in different platforms improves the accuracy in detecting XBI. By observing DOM mutations during the replay, X-CHECK also designs an incremental cross-browser detection algorithm, which only detects mutational content of Web page. This algorithm improves the performance in detecting XBI. The empirical evaluation shows that X-CHECK is effective, efficient and improves on the state of the art, and can provide useful support to developers for diagnosis and (eventually) elimination of XBI.