I would like to move a tab (from new-tabs.js) one position to the left or to the right. Maybe it's easier
to change the order of the buffers, not the tabs, so that C-x b (switch_to_buffer) shows also the new order. 

Some code and implementation ideas are in this thread:
http://www.nabble.com/Reorder-tabs-or-buffers-td23085091.html