Firefox add-on – Ctrl+Tab navigation and All Tabs panel.
Shift+)Ctrl+Tab navigation for Firefox tabs:

• Tabs are presented in most-recently-used order, similar to Alt+Tab on various operating systems
• Releasing Tab and pressing it again moves to the next preview
• Pressing W closes the selected tab
• Releasing Ctrl switches to the selected tab
• Hidden preferences: browser.ctrlTab.mostRecentlyUsed, browser.ctrlTab.recentlyUsedLimit, browser.ctrlTab.smoothScroll

• Firefox: 3.0pre – 3.1b1pre