Windows 7 gives Firefox 3, IE8 speed boosts, while Firefox 3.5 slows down ! The first tests comparing browser performance between Vista and Win7 present good news for production browsers, but bad news for the most popular beta.

In preliminary Betanews tests Tuesday comparing the relative speeds of major Web browsers in Windows Vista- and Windows 7-based virtual machines, not only did the general performance of Microsoft Internet Explorer 8 improve by about 23%, but the latest production build of Firefox 3.0.10 appears to improve its performance by 17.5%.

This despite running in a Windows 7-based virtual machine that we estimate to be 12.1% slower overall than a Vista-based VM hosted by the same environment.

These are the initial findings of Betanews’ experiments in how the architecture of Windows 7 may or may not influence the performance of major Web browsers.

We wanted to see whether Win7 made browsers faster or slower, and doing that meant hosting browsers in virtual environments whose relative speeds with respect to one another could be normalized.