Among the most significant new features there is the implementation of click-to-play, which is designed to prevent vulnerable versions of plugins to run without user’s explicit consent. This means that plug-ins are no longer loaded automatically and the user has to click on them to load them up. On Mac OS X 10.8 there is support for notification center.
Another big change in Firefox 17 is the preliminary support for the new Social API with a set of new features developed by Mozilla. Its purpose is to allow developers to integrate social services into the web browser in a manner suitable for the users.