I have to admit that I've developed a nasty habit. When I want a new browser window, I shift+click the Firefox icon to make a new window of Firefox. Lately, though, I've been really wanting to get in the habit of just creating a new tab instead of creating a new window.
I'm wondering if there's a way I can change what the keyboard shortcut actually does, e.g. can I have it start Firefox with some sort of shortcut that would prompt it to start a new tab rather than a whole new window?