Tree style tab [0] exists, and you can change Firefox's userChrome.css [1] to hide the tab bar. To make old tabs sleep (not quite delete, but close), use Auto T

Tree style tab [0] exists, and you can change Firefox's userChrome.css [1] to hide the tab bar. To make old tabs sleep (not quite delete, but close), use Auto Tab Discard [2]. 0 - https://addons.mozilla.org/en-US/firefox/addon/tree-style-tab/ https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta... 1 - https://gist.github.com/akersten/8fa7d36960b10c5ae18c01ada3d778bd https://gist.github.com/akersten/8fa7d36960b10c5ae18c01ada3d... 2 - https://addons.mozilla.org/en-US/firefox/addon/auto-tab-discard/ https://addons.mozilla.org/en-US/firefox/addon/auto-tab-disc...