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.

Comments:
Wayne Morrise
11/09/2011 06:37 pm
I think it is good in my Firefox and Google Chrome. Maybe it is a problem in the version of the web browser, because I experience it and I only update my browser and it performs good after the update.
Joseph Aucoin
12/20/2011 10:58 am
I too am having the same problem . . is there any manual fix for this?
adeel
09/11/2012 05:51 pm
hey.. i have tired it on opera, firefox, chrome and IE 4. but its not opening in any of them.. please do something.. i have to put my website to google webmaster tool.. plz do something.. and help me out how to open it.. thanks..
brat
02/02/2013 08:44 pm
googles chrome isnt even opening google home page what a frickin waste what the hick is going on with google!!!!!!!!!!!!!!!!!