You can clone with
Ctrl-enter should immediately execute the current line, and move to a new line within the new cell, and it does in Chrome. But in Firefox, it seems to clear the current line without executing it, and move to a new line.
Tested in Firefox 6 (Ubuntu), with Tornado from git today.
Not quite my experience. Also, there's no new cell, ctrl-Enter is for executing a series of commands in one cell (e.g. ls, cd, etc. things you don't actually want to be part of the notebook).
In Chrome: ctrl-Enter executes the cell, and leaves the input selected, so typing the next command will clear it (this is the correct behavior).
In FF6: ctrl-Enter executes, but clears input and adds a newline, which it shouldn't. It is essentially equivalent to the Chrome behavior followed by hitting 'Enter'.
OK, for some reason when I tried it before I didn't think it was executing, but having tried it again, it seems I was wrong about that.