If you install Greasemonkey for Firefox, you can add a script that sets some keyboard shortcuts for Google search. The script works even for the localized versions of Google.
You'll see that each search result has a digit in front of the title. This works only for the first 10 results from a results page, so it might be a good idea to stick to the default number of search results (which is 10).
You can also go to the next page of search results by tying n and go back to the previous page by typing p. To edit the query you have two options: either type e to select the query, so when you type something the query will be replaced, or type a to append something to the query.
A very cool feature is the tab mode: if you type t, the numbers will be highlighted in green and search results will open in new tabs.