Hi djdave238, normally the "+" button clings to the last tab once you exit out of Customize mode. If it doesn't, could you go back to Customize and see if there are any controls between the last tab and the "+" button which could explain the gap?

If you can't find any reason for the problem, there is a "Restore Defaults" button at the bottom of the tab to reset the toolbar area.

If that doesn't help, can you think of any custom style rules you may be applying to the tab bar in a userChrome.css file? By default, there is no such file, it's something you would have needed to add yourself.

Note that the new tab + button is customizable and can be placed on other toolbars where it appears as a new tab button with its own icon. On the Tab bar there are two such icons possible depending on whether the tab bar isn't fully filled directly after the last tab or when the tab is full this button is located at the far right end. The new tab button would normally snap automatically to the position after the last tab, so make sure that not too many tabs are open when you are in customization mode.