I used to have tab trees and they are amazing. The extension I used had some stability / slowness issues and I also like having nothing on the sides of the webpage.
I would still appreciate a tree view that shows when clicking a button when I need it, maybe something like the Netsurf History that shows when long clicking on its previous button (by the way, this next/previous tree feature of Netsurf is awesome, it would be great to have this as is in other browsers).
But I usually have many tabs and Firefox is usable without tree tabs.
I use CTRL+tab to cycle through most recently used tabs. If you enable the browser.ctrlTab.previews about:config setting, you get a nice alt+tab-like window.
The order of tabs in ctrl+tab is changed when using browser.ctrlTab.previews (from simple in order tab circle to circle through most recently used tabs, lastly used first). I have become dependent on this to the point that Chrome or Firefox without it feel like they get in my way when I browse.
I also from time to time used the list of tabs provided by the ctrl+tab previous window, but it seems to have just disappeared in a recent Firefox update?
Anyway, I find that the most efficient way to go to a not so recently-used tab is to just search for something in its title or its URL in the URL bar (CTRL+L) and use the "go to tab" feature (and I disable search engine suggestions in the URL bar). And if you closed the tab, the page will be proposed because it is in the history. Chrome's URL tab just feels useless in comparison.
The URL bar of Firefox and its CTRL+TAB tab preview feature / cycle order are two killer features for me. Losing them would be painful.