Mozilla released Firefox v25 today, the latest version of their Firefox browser. The biggest change from Firefox v24 to v25 is a new feature in the mobile version of Firefox called guest browsing.
Say you hand your phone to your friend to use - just start a "guest session" of Firefox and he or she won't see any of your bookmarks, passwords, etc. Not only that, your friend's surfing is secure because anything done in the guest session is removed when the browser is closed. Pretty handy.
You won't see a lot of changes in Firefox for Windows or Mac. There were some behind-the-scenes improvements that developers will like, like Web Audio support and the ability for add-on makers to add URL indicators, something that wasn't possible before v25.
You can download Firefox v25 here, or just watch for the update notification next time you're using the browser.
In addition to the new features I already mentioned, over 500 individual bugs were fixed, all of which you can read about on their Firefox v25.0 Bug Fixes page. A highlight of new features and major fixes can be found here.