This button can migrate to other toolbars, or return to the button palette with the unused buttons. Try using the Customize feature:

right-click a blank area of the tab right, then choose Customize...

The attached screen shot (third image) shows the appearance of the new tab button when it is on another toolbar or in the button palette. Can you find it and drag it back?

Edit: By the way, my button is always after the last tab, not next to the current tab. If yours moved around based on your active tab, that might have been a feature added by an add-on.

Thanks for the reply. My button was after the last tab until I upgraded. What I did was restore to default tool bar and the button was there. I then re customized my tool bar the way it was.

Thanks again for the help. Jim