Microsoft Internet Explorer 9 Preview 4 in the wings?

It sounds like Microsoft is going to deliver one more developer preview of Internet Explorer (IE) 9 before it rolls out the first public beta of its next-generation browser in September.

On August 4, I saw a blog post appear and just as quickly disappear before I could read it that mentioned the new preview.

Update: Yes, the new, fourth developer preview is available on the IE Test Drive site as of August 4. The IE team has posted a blog entry with more on what's in IE 9 preview 4.

So far, Microsoft has delivered three IE 9 previews: The most recent was delivered in June. In March, company officials said to expect the company to deliver developer-focused previews of its browser roughly every eight weeks.

At Microsoft's recent Financial Analyst Meeting (FAM), Chief Operating Officer Kevin Turner said to expect Microsoft to deliver an actual beta of IE 9 (not just another preview) in September. (The rumored public beta date has been August.) Microsoft officials still haven't said when to expect the final IE 9, but many company watchers expect that to happen in 2011.

So far, Microsoft's test builds of IE 9 have shown off the progress Redmond is making on the standards and performance fronts. The company hasn't shown off any hints of what the new user interface for IE 9 might look like.

If the aforementioned blog post headline was accurate, Microsoft is continuing to improve its Acid3 compliance (even though company officials have insisted that Acid3 isn't really a useful test). Word is the company could claim 95 percent compliance with Acid3 with IE 9 Preview 4.

I've asked Microsoft if and when it plans to deliver another IE 9 preview. Stay tuned....

Update No. 2: My ZDNet colleague Ed Bott has more details about it, including Microsoft's explanation of why it's scoring a 95 with Acid3 and won't get to 100. This is the last developer-focused preview before IE 9 hits beta next month, the Softies are acknowledging.

Update No. 3: Microsoft has made some changes to the JavaScript engine (codenamed Chakra) with this preview release. According to Microsoft: "In the fourth Platform Preview, we’ve moved the JavaScript engine inside IE9. With this change, communication between the browser and script engine is now direct, which significantly improves performance for real world websites. We now have a single DOM, shared across all browser subsystems including JavaScript."