Comment 1 for bug 905078

To find a reasonable new behavior for this, I looked at other browsers and completion implementations.

The way GTK behaves in the analogous situation in its file chooser is (with up/down arrow keys, as it considers tab "next widget" or "complete to the next ambiguous point") to move from bottom downward to the entry itself, and then down again brings focuses the first entry. Going up takes the same logic, with the entry itself between the first and last completions.

Firefox does the same thing (wraps around in both directions with the entry itself as an intermediate), but allows tab like midori does.

Chrome only allows the arrow keys for up/down in selections and doesn't wrap around at all. It interprets tab as "use the selected completion", any printable character as "use the selected completion and append this character", and escape as "return to the pre-completion text".

I'd think it'd likely be best to mirror the GTK/Firefox behavior, as it'll be more consistent with other GTK programs and therefore more predictable to users.