It used to be that when you double-clicked - or started typing - inside of a box that had a familiar label (i.e., you'd filled out a box with that field label in some other form lately), you would get a drop-down list of suggestions based on your input from the past. Lately, in Firefox (3.6.13 is what I have), I've been getting the drop-down list with a bunch of empty (invisible?) suggestions, yet with the "Form History" notation next to each of them. It's not that big a deal, but I just wanted to know if anyone else is experiencing this, and that I (or my computer) am not going crazy...
I'm using the same Firefox version and I don't see that problem. Did you possibly delete your form history by mistake? If you've gone to "clear recent history" lately and didn't uncheck the form history box you may have deleted it. Other than that I'm not too sure.