Existing mobile platforms landscape evolves very quickly, as the big players in the field and the research community are challenged to develop novel solutions with minimal costs of application development and possibility to support natively mobile web applications. This process to a great amount has been driven by the presence of Android, an open-source operating system developed by Google. In this article we overview two promising platforms that are both open-source and web-based: Firefox OS (contributed by Mozilla) and Tizen (backed by Samsung and Intel), and compare their security features with those of the Android OS.