(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

Ctrl+Shift+A / Cmd+Shift+A shows all tabs in a grid:
* Shows all open tabs
* Tabs can be closed by middle clicking

* Search field filters tabs based on their titles and addresses, Enter selects the first tab