What is Caret Browsing mode in Firefox?

Like when you were typing the question, it's the little blinking | symbol. Hit F7 to turn it on, it'll let you more easily copy text with the keyboard, if that's your thing.

Caret Browsing lets you use standard navigation keys on your keyboard e.g. Home, End, Page Up, Page Down, and the arrow keys to move around within a webpage (just like you would move around in a word document), instead of using the mouse.