Since I started using FARR I'm used to hitting "enter" when the first option is the one I want. Problem is, I do the same thing in Firefox: In the newer versions, you can type part of the middle of a URL or part of the title of a page you've been to (or bookmarked) and it will give a drop-down list of matches. Then you hit enter (like in FARR) and you get a search for the term you typed instead of the first option in the list. I don't use search from the address bar (or as it's now called, the "AWESOME bar") so this extension is perfect.
It tries to detect if you've typed a URL and if so it moves the focus back to the bar itself rather than the first list item. A few times I've found that if I typed too fast it selected the first result rather than the URL, though.
This extension disables a few uses of the AWESOME bar that I didn't use such as quicksearches and bookmark keywords
By the way, I searched the forum and found a mention of this extension buried in a list of favorite firefox extensions, but I thought I'd bring it to the attention of FARR users like myself.
There is a snippit of AHK code in one of the comments for achieving the same thing, by the way.