Firefox is at v18? Last I knew it was at v5. Guess they didn't waste any time in their quest to catch up with Chrome.
The version number is meaningless. What is meaningful, however, is getting millions of people to help test beta browsers. If Chrome is your browser of choice then help test the Canary builds (https://tools.google.com/dlpage/chromesxs)
Browsers are not just rendering engines.
On Windows, Chrome does a good job auto update in the background. Firefox am not so sure but they too are working on some kind of auto update. Good for them, not being stubborn, and implementing a good feature that their rival has.
Good for Chrome that they aren't suing others trying to implement auto update. :-)