Toolbar buttons to move back and forward in the tab list like the Ctrl pgup / pgdn shortcuts. Also close next / previous tab with Right-click, and Middle-click makes them custom new tab buttons.
Here are the features of Active Tab Switcher:
- Left-click moves back or forward in the tab list
- Right-click closes the next or previous tab
- Middle-click opens custom new tab urls
Learn more about this great add-on at the Firefox Add-ons website.