Thanks for the replies, though I didn't stop to think about overriding the default browser tabbing. Is there an easy way to do this from within Construct 2's event sheet, or is this something I'd have to right a plugin or external JavaScript for?
My logic is currently something like this, and it appears as though the built-in browser tabbing is interfering with this:
On key code 9 pressed
----if text0 has focus, set text1 focus
----else if text1 has focus, set text0 focus