There are a few methods to accomplish this. Here's one:
Make sure you are NOT signed-in to google.
Then go to http://www.google.com/ncr
Click on Options ()in the upper right-hand corner
Select Search settings scroll down to the bottom of the page and click:
That should do it. The preferences are stored in a cookie which means this procedure needs to be done on each computer in each account on each browser that you use. So, if you only use Firefox and one computer, you only have to do it once. If you have two accounts, access three computers and use four browsers, you'll need to do it 24 times.