In January 2010 ...
Internet Explorer 29.10%
(no other browser got over 1%.)
And for operating systems ...
As you can, our audience is considerably more tilted toward Mac users than the Internet at large, though Mac usage has grown considerably since mid-decade. And that's a story in itself.
What continues to surprise me is that rapid decline of Internet Explorer. Only a few years ago, IE was basically the only browser there was, with the exception of a few marginal browsers with small but devoted user bases. Now, as you can see, Firefox is by far the dominant browser among our users.
Now, some of that is because we have so many Mac users. And Microsoft discontinued IE on Mac a few years ago. But it's not all that. Last Fall, I did another one of these posts, and looked at the browser stats going back to 2007. And the trends are striking. Back in late 2007, IE was still the biggest browser among TPM Readers. A year later, Firefox was a bit ahead. And by late 2009, Firefox held a 10 point lead.
Chrome usage is also growing rapidly. In September 2008, it was 2.07%. A year later it was 4.19%. And now it's 7.17%. I'm one of them. My initial reaction to Google's Chrome browser was not completely positive. But I've now made it my default browser on all my computers.