Mac-based browsers have had a growing share of web use, but a new report shows an odd drop in that number for the month of November, 2009.

The new data from NetApplications appears to indicate that the first full month of Windows 7 availability took a hit on the Mac web share. Windows 7’s share nearly doubled to 3.98% of all Internet traffic, while the Mac dropped 0.16% at the same time, according to Electronista.

Mac users traditionally get a web share bump in December as more users spend time at home with their Apple systems compared to the Windows-based systems they use at work. In recent years, Mac users have even contributed to the overall Windows share of web use thanks to Apple’s Boot Camp being part of OS X, or from users running Windows-based browsers inside virtual machines like Parallels Desktop.

Windows Vista still got no respect, losing only 0.23% web share versus Windows XP, which lost 1.45%, another sign that many users skipped over Vista in favor of Windows 7. Microsoft also continues to lose in browser share, with Internet Explorer dropping another full percent to reach 63.61%, its lowest ever.

Meanwhile, the popular Firefox now has nearly a quarter of the market, jumping to 24.74%. Safari declined only slightly to 4.36% while Chrome gained almost a half point to 3.92% and Opera rose to 2.31%.