Rated 5 out of 5 stars

@Watchmanz: Super DragAndGo hasn't been updated since before Fx2 (it's not even fully compatible with that; drag-to-search doesn't work with Fx2), so it is highly unlikely that it will be updated for Fx3

For Fx3, you can try QuickDrag:
https://addons.mozilla.org/firefox/6912