- Edited
The rough idea for animations would be slightly complex but it would roughly look like getting the areas of both the targetted tab to be focused and the currently focused tab, take all of the tabs in between them and shift them to the right or left depending if you are targetting the left side of the current tab or to the right.
On the second to last demonstration, the last two tabs are left untouched in terms of tab horizontal positioning, while on the final one all of the tabs are shifted to the rijght to make space for the first tab's expansion and transformation into the address bar. And vice versa for the right side being transformed into the address bar and hence the entire left side of the browser becoming shifted to the left.