Today, Microsoft is releasing the final major pre-release milestone of Internet Explorer 9, a release candidate build that the company tells me is very, very close to final. I've only had the RC build for a short time, so a full review isn't yet possible. But I'll save that for the final release of IE: For now, let's take a look at what's new in the release candidate.

User interface changes

With IE 9, Microsoft is offering a slightly refined UI over its predecessor, with a new OneBox that integrates web site navigation and searching into a single control, as is the case with many other popular browsers. Part of the goal of this redesign was to minimize the browser "chrome," giving more onscreen real estate to the sites and web apps you're visiting. Based on feedback from the Beta release, Microsoft has made some changes to the UI.

General UI changes. Microsoft has further decreased the space that the top navigational controls occupy, giving a bit more space to web site content. Microsoft says this provides more space than does Chrome, which is true, but only when the browsers are used normally. If you create a web site shortcut in Chrome, the resulting window uses no browser Chrome at all, whereas IE pinned site windows retain much of the browser Chrome, leading to less space for content.

Tabs. While most users are working with five or fewer tabs at a time, according to Microsoft, a vocal contingent of power users complained that placing the tabs next to the One Box limited the number of tabs they could easily work with. So in the RC, you can now choose to move the tabs to their own toolbar below the One Box. This toolbar extends across the entire width of the window.

Microsoft also made it easier to close tabs that are not currently being viewed. Simply hover over the tab and click the close box; you no longer have to select that tab first.

One Box. Microsoft has refined the look and functionality of the One Box, providing a new layout and look for the in-box "glyphs" (icons, essentially) that appear within it. You can now also easily refine search results by clicking the search (magnifying glass) glyph to edit a previous query.

Notifications. One of the issues I had with the IE 9 Beta was that some of the notifications were annoying because there was no way to select an "always ignore" option. These notifications have been nicely refined in the RC, however. So some notifications will auto-disappear after a set amount of time, while other, more important, notifications will alert users to their presence with a "gleam " effect that is reminiscent of the behavior of Windows 7 taskbar buttons. The download notification is a good example of this.

Menu bar toggle. When you right-click the empty area of any toolbar in IE, there is now a menu bar choice so you can easily toggle this menu on if you'd like.

Pinned Sites. IE 9's ability to pin popular web sites and apps to the Windows 7 taskbar is a powerful one, and it makes these sites look and behave more like true Windows applications thanks to optional features like customizable jump lists, taskbar notifications, and more. In the RC, these capabilities have been enhanced. You can now pin multiple home pages to a single pinned site, so that when the taskbar button is clicked, each page opens in a tab of the resulting browser window.

And while this is currently hard to demo since site makers are working to implement this functionality, Microsoft has extended the programmatic capabilities of the browser to support site pinning from on-page elements. So, for example, a site could provide a button that could be dragged to the Windows 7 taskbar in order to pin the site.

Finally, Microsoft is enabling InPrivate mode for pinned web sites.

Tracking protection. Microsoft previously announced that it would implement a "do no track"-like feature in the IE 9 RC, but at the time it said it would not provide an integrated list of advertisers to block. Since then, there's been a dramatic improvement here: Yes, you can still download a number of prebuilt third party tracking protection lists if you want. But there's a toggle in the tracking protection UI that allows the browser to automatically block advertisers that follow you around the web. Thank you, Microsoft: This is exactly the type of thing I was looking for. And I recommend that all IE 9 RC users give this a shot: You can find it in Safety, Tracking Protection, Settings, Automatically Block.

ActiveX Filtering. Also new to IE 9 RC is a way to block ActiveX controls for all sites and then later re-enable them on a site by site basis, turning on access to these useful but potentially dangerous controls only on sites you know and trust.

Other improvements

In keeping with the improvements offered over the numerous pre-release IE 9 milestones, the RC version offers better performance, both from an overall perspective and with regards to specific features like the JavaScript engine. Microsoft claims that the RC version offers 35 percent faster JavaScript performance, or about 20 times the performance of IE 8 on the same benchmarks. Overall, over 2,000 performance-related changes were added to IE 9 between the Beta and RC releases. This should result in faster overall performance around such things as IE load time, web page load time, and so on.

Additionally, the IE 9 RC now offers dynamic GPU rendering, so that it can switch automatically between software-based and hardware accelerated rendering based on the performance characteristics of the PC. The net result should be faster and more reliable performance for all users. And for those using GPU rendering, IE 9 will provide better battery life on mobile computers because the system's CPU can remain idle.

But wait, there's more...

There are additional improvements in the IE 9 RC around standards interoperability, of course, and in other areas. But I think it's more important for web developers and site maintainers to understand that the final release of IE 9 is right around the corner, and if you haven't done any work to ensure that everything works properly in this browser version, you're running out of time. IE 9 has had the faster adoption in IE history, with over 25 million downloads since September. This is going to be a popular browser, and you're going to want to be in on it.

For users, IE 9 is a near-final look at Microsoft's vision for a modern web browser. Again, I've only been using the RC version for a short while, so I'll need more time to determine whether it meets my own needs for performance, compatibility, and functionality. But so far I like what I see quite a bit. And if you're reading this site, chances are you will too.