OS X :: Can't Type To Folder In Snow Leopard

I've had this problem since I upgraded to SL and I'm finally looking for a solution, as it's mildly annoying So anytime I'm opening up a file browser window within an app - say, to upload or save a file in Firefox, or to open a file in any old program - I used to be able to navigate to a folder on my keyboard by typing the first letter or two of the name. Now, however, when I try to do that, nothing happens except the Mac makes that dull "thud" sound. Now, if I navigate inside a folder (by pressing the right arrow key) and then go back out (press the left arrow key), then it works like a charm. But what a pain!