From the "shiny new objects" file:

The first alpha for Mozilla Firefox 3.1 (codenamed Shiretoko) is now out boasting a number of incremental improvements over the recent Firefox 3 release.

There is a new tab switching behavior, improvements to the 'awesome' bar (aka the Smart Location Bar), as well as some web standards improvements.

Personally speaking it's the improvements to the awesome bar that have me interested in Shiretoko alpha 1. There are some quirky behaviors in how the bar permits tagging in my view and it looks like Mozilla developers are keen on making the awesome bar even more....well...awesome.

When it comes to new web standards - that's a good thing for the web community, but inevitably unless other browser vendors pick up the same standards - they end up having little practical utility (unless a web developer is only going to focus on Mozilla).