https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta...
I use it with Tab Mix Plus for extra tabby features, like progress bar on the tab, tracking unread tab state, lots of undo close tab slots, forcing popups to show up as tabs, etc:
https://addons.mozilla.org/en-US/firefox/addon/tab-mix-plus/
The tab panorama feature is built in:
https://support.mozilla.org/en-US/kb/tab-groups-organize-tab...