Firefox 25 came out a few days ago mostly with UI tweaks, the usual smattering of features that the typical user won't see, and security fixes. The biggest feature for Firefox 25 is the Web Audio API support. Read more.
Further details on Firefox 25 on the release notes.
Firefox 26 should be more interesting since it's the first Windows 8 optimised build. The Social API is also getting a nice improvement allowing multiple services to run simultaneously.