When I search something I often rephrase search query or use other search provider. Sometimes I search for a correct bookmark in the address bar and choose the wrong one.
If in the first case I can just use search input on page to change the query a bit, in others I must retype everything in the address bar again (or copy-paste it, which is still not that cool).
It would be cool if the address bar could restore a previous search query (automatically, or by showing an option to restore it, like 'Go to tab' one), mobile firefox already allows you to change query from address bar and that is useful
