In the last few years, a number of new security features have become available to web developers (e.g. Content Security Policy, Strict Transport Security) and a few more are coming up this year (e.g. Referrer Policy, Subresource Integrity).
As a browser vendor and a member of the W3C WebAppSec working group, Mozilla is busy extending the web platform to provide the tools and features that developers and users need in 2015. In addition to that, the non-profit behind Firefox is experimenting with new ways to protect its users, building on Google's Safe Browsing technology to defend users against tracking.