Small Torbutton icons should be 16x16 pixels
Although tor-disabled-16.png, tor-enabled-16.png and tor-update-16.gif sound like 16x16 icons they are in fact 18x18 icons. That should not be the case as this might cause some weird behavior (see e.g. https://trac.torproject.org/projects/tor/ticket/8478#comment:13).