What determines the first site displayed when I start typing?

For ages, when I type the letter "i" in my address bar, the site instapundit.com shows up, which makes sense because I visit it multiple times a day, thanks to its frequent updates.

Yesterday, I typed "i" again and the site "inspiredm.com" comes up. I don't remember ever visiting that site before, and it appears to contain nothing I'm particularly interested in seeing more than once.

Any idea why this changed, and how I can change it back?

David