Only six weeks after Firefox 9, the latest version, Firefox 10, is now being downloaded onto users' machines. As far as end users are concerned, the key improvement is probably that this, and future updates, won't break plugins. Basically the change is more one of policy than mechanism in that it simply assumes compatibility.
The almost automatic breaking of extensions a feature of the new rapid update cycle that was irritating users. A better Firefox every few weeks is a nice idea. but not if each time it tells you that extensions vital to the way you work are out of date.
What is really interesting is that the main new features of note are aimed at the developer, not the user. Is this the start of the browser developer wars? After all, if you have to implement a standards-based browser how can you distinguish yourself to the end user?
Developer tools on the other hand are features that you can make your own and hence distinguish yourself.
The new Page Inspector extends the feature provided by Firebug to allow you to see the structure of a page as you move the pointer onto different elements. To see how it is better watch the following video:
At the end of the video there is mention of Scratchpad which has, of course, been available in earlier versions of Firefox. Overall however, the integration of the developer tools makes them much easier to use and there is more to come. Mozilla is working on a WebGL 3D display of the DOM which might make it into version 11.
As well as tools, APIs have been added and updated. The most important is the Full Screen API which allows web apps to break out of the browser and use the entire screen area. Also new is support for CSS 3D transformations and the Battery API.
Along with the desktop Firefox 10 we also have the mobile version released at the same time with improvements to its touch input.
One interesting problem is that Mozilla's new speedy release policy has resulted in Firefox reaching version 10 much sooner than anyone could have predicted. As a result the two digits in the User Agent Id are causing some scripts to crash or misidentify Firefox.
You think we might have learned not to assume such simple things.