css overflow - only 1 line of text

If you want to restrict it to one line, use white-space: nowrap; on the div.

If you want to indicate that there's still more content available in that div, you may probably want to show the "ellipsis":

text-overflow: ellipsis;

This should be in addition to white-space: nowrap; suggested by Septnuits.

Also, make sure you checkout this thread to handle this in Firefox.