I haven't looked at new-tabs.js, but as far as I understand, it is designed to be more flexible, whereas
tab-bar.js was something I just quickly put together to appease requests for a tab bar (and I don't use
it myself).  Is there any difference in the basic CSS/DOM layout stuff between the two that is the reason
for the flickering being fixed, though?  It would be nice to understand exactly what is causing the
flickering and how the flickering is avoided (so that someone playing with the CSS rules later doesn't
inadvertently cause flickering), but I suppose as long as it doesn't flicker, that should be good enough.