Firefox OS 2.5 offers add-ons, private browsing and tracking protection, and a "pin the web" allowing users to pin a site or page to a home screen.

Today we have made Firefox OS 2.5 available worldwide. We are also making an early, experimental build of the OS — Firefox OS 2.5 Developer Preview — available for developers to download on Android devices. Mozilla Releases Firefox OS 2.5, Developer Preview [hacks.mozilla.org]

[mozilla.org...]