Browser save session on quit

A proof of concept for saving the browser session on close/quit. Sometimes, I do want to save my session (i.e. tabs), but more often, I don't. This solution would be perfect for me: I could save my session only if I want to.

To clarify: the browser will auto-close after the timeout. The loading indicator indicates the time left to make a choice.

Should I use 'close' or 'quit'?