Firefox OS 2.5 brings support for add-ons, private browsing with tracking protection, Pin the Web support, and more.
In regards to this Firefox OS 2.5 Developer Preview for Android, Peter Dolanjski explains, "You’ve asked how to get involved with the Firefox OS open source project. To date, it’s only been possible to download and explore the latest versions of Firefox OS on specific hardware, such as the Flame device. We’re now working on making Firefox OS more widely available. The Firefox OS Participation Hub provides up-to-date information on getting involved with Firefox OS . The B2G-installer add-on lets you flash a full port of Firefox OS on to an Android device."
More information over on Mozilla Hacks.