Tabindex 0 doesn't come first, that goes to tabindex 1 (note that this varies based on browser implementation). The usual effect of tabindex 0 on pages with no other specified tabindex is to get the untabbable elements showing up in the tab order in DOM order (although again, browsers are inconsistent). When I tested this in FF, Opera, and IE with tabindex 0 the facets showed up last, which is DOM order.

http://www.w3.org/TR/html401/interact/forms.html#adef-tabindex