Good idea but... Rated 3 out of 5 stars
Not sure about the other engines but this causes google to use "I'm feeling lucky". An option to turn this on or off would be nice. Also would be nice to be able to edit the search string, I know I could go to about:config but then I'd have to look up the thing I have to edit first yadda yadda.. that's why I installed this.
When you choose "Custom" you can edit the current search string.
Comment on "Lucky" search noted for next versions.