Firefox 15 comes with the usual array of new features, more if you don't mind poking under the hood and enabling them. On top of that, Firefox got plenty of performance enhancements. These are harder to spot though, you can see a new feature in front of you, but it's harder to "see" speed improvements, unless they are huge.
the latest enhancements to WebGL in Firefox 15, Mozilla put together BananaBread. BananaBread is a playable demo that shows just what browsers are capable these days when it comes to games.
Apparently, that's not the case. Not only that, it works perfectly thanks to a number of new technologies and features in Firefox. WebGL is now more optimized than ever. Firefox 15 also brings support for compressed textures, significantly reducing memory and bandwidth consumption.
Apart from the WebGL improvements, Firefox 15 also comes with a new high-precision timing API which comes in very handy in games, especially shooters where everything is measured by the millisecond.
Firefox already supported the FullScreen API (self-explanatory) and the pointer-lock API which enables the browser to capture the mouse, essential for first-person games.
In the end, none of this means much. What is important are the games so the best way to judge whether Firefox is up to spec is to play something, the BananaBread demo
being a good place to start.