After playing around a bit with
Mozilla Ubiquity I found that it comes with a command for searching for Google Maps (command "map") but does not have a command for searching for OpenStreetMap maps.
Well, after a taking a look at other Ubiquity Commands, I found out that it's rather easy to create your own command, and so I did:
Ubiquity OpenStreetMap Command.

The result is a query to the OpenStreetMap namefinder server:
Simply install this command (optionally auto-update as I may adapt the code over time) and you can search for OpenStreetMap geolocations using "osm Linz" or, alternatively, "openstreetmap San Francisco". Please be patient with the OpenStreetMap server, which seems to be a bit slow in finding the correct location for some name.
Drop me a line, if you like the command, or if you have suggestions how to improve it (preview?)!