wow, I'm using the "dragable content script" and I have the same issue, in Firefox the input type text can't be written on it.... if anybody got an "universal" solution, pls let us know!
edit: but for now, I'm going to use the OP solution, onclick="this.focus();".
edit2: oops, but what about the input type="submit" ?? ...
we gotta have better solution, help guys pls