If you want to use a DOM node from the page in the console:
- Right-click the node in the Elements (or Inspector in Firefox).
 - Click on Store as global variable (or Use in Console in Firefox).
 
The Console opens up, pre-filled with a new variable name (something like temp1) which you can use to refer to the node any time you want.
Note that if you only want to refer to the currently selected node (and not create a new variable), you can also use $0 in the console.

Thank you Austin Gil for sharing this tip on Twitter!