Changes

Clearly this code has some problems, since we've completely broken addTab. Let's look for clues in the '''Error Console''' (Tools > Error Console). Notice the following exception appear whenever we try to add a new tab:

Now we know how to find errors our JavaScript produces. Looking back at our code, it's clear that that '''childNodes.length''' is not zero, but 1 by default (i.e., there is always at least one tab, even if it isn't visible). A quick modification to the code, and we get: