In FireFox, how can I make new windows start blank with the focus in the URL bar?
Update Note: The original answer was applicable to Firefox version 50, and somewhere along the way Mozilla added what's shown directly below. (From Firefox version 66.0.5).

Firefox (menu) > Preferences… ⌘` then click Home and set Homepage and new windows and New tabs to: Blank Page







Original Answer

To have Firefox open a new window to a blank page, you'll need to set the Home Page to about:blank under General preferences (about:preferences#general in the Address bar).





Then when pressing ⌘N, this is what a new window will look like when it opens: