steveninc on "How do I fix my double line spacing?"

I have just installed wordpress on my development server and when I create or edit a new post, all lines are double spaced.
That is to say that the carriage return is entered twice.

I would like to set my editor to single line editing.
Where can I change this setting?

I am using firefox 3.6.8 on windows7 x64

I appreciate the help.