There are confirmed reports in the Google Webmaster Help forums that Google Webmaster Tools is not loading in all browsers.
Pierre Far of Google confirmed the issues saying:
Thanks for the report. We know of an issue affecting how some browsers fail to display the new home page. Just to be sure what you're experiencing is not a new issue, can you please take a screenshot of how it's breaking for you? It would also help if you mention which version of Windows you're running.
Here is a picture of how the home page loads in Internet Explorer 9 using Windows 7:
There is not estimate time for a fix for this bug. This isn't being widely reported or complained about either.
Forum discussion at Google Webmaster Help.