Microsoft this afternoon is issuing the first "release candidate" version of the upcoming Internet Explorer 8, moving another step closer to the official debut of the browser. The company isn't yet saying when that final release will come.

Internet Explorer still dominates the worldwide browser market, but Firefox and others have been making sizable advances -- boosting the stakes for Microsoft as it prepares IE8 for release.

The biggest new features, such as Web Slices and Accelerators, were introduced in previous Internet Explorer 8 previews. But the company is continuing to make adjustments as IE8 moves toward final release. Here are some of the changes that have been made in Internet Explorer 8 Release Candidate 1.

Adjustment for incompatible sites: One of the big changes in the new IE is Microsoft's shift toward compliance with Web standards. The problem is that many sites written for older IE versions aren't compatible. In the previously released IE8 Beta 2, the company offered a "Compatibility View" button to switch back to a mode that works with those sites.

"As we looked at that telemetry data, we learned that users were pushing that button a fair amount, and they were pushing it for fairly well-known sites," said James Pratt, an Internet Explorer senior product manager.

So as part of the changes in IE8 RC1, the company has come up with a list of sites that it has learned, through that feedback, need to be run in compatibility view, for now. Those sites will run in that view, out of the box, unless the user opts out for a particular site. As more sites are written to standards, Pratt said, they will increasingly be shifted to run in Internet Explorer 8 default mode.

Browser performance: Microsoft spent time optimizing the performance of the browser for different types Web sites and underlying code. Pratt says users should see "very, very comparable" speed in IE8 RC1 when compared to competing browsers.

Smart Address Bar: This feature previously let people type keywords into the address bar to bring up items from their browser history, favorites and feeds. The company found that many people weren't using the bar to access feeds. As a result, Microsoft removed feeds from the results by default, which lets IE8 RC2 show more information from history and favorites.

InPrivate Filtering: This is the new name for the feature previously known as InPrivate Blocking. The feature limits the ability of third-party content providers to track the activity of users as they move among different sites online. The new browser also gives users more nuanced control over which third parties can track them, and to what extent.

Previously, the feature was available only when a user had activated InPrivate Browsing -- known colloquially as "porn mode" -- which keeps the browser itself from retaining history, cookies and temporary Internet files. Now, in IE8 RC1, InPrivate Filtering is also available during normal browsing.