How to change the form input tabbing order

I'm using Boostrap on a simple sign-up form and I'd like to setup the order of the tabbing order. It currently skips the "Sign up" button.

I did added tabindex="1" for each input field (e.g. 2, 3, etc.), including the submit button, but it doesn't works.

Here's a jsFiddle.

It seems to work in Opera, but not in Safari or Chrome. Any work-arounds?

UPDATE: Works in Chrome, Opera, but not Safari.