[tonetheman]

What is the name of that extension? I searched and get over a thousand results. Thanks!

[andrewflnr]

"Tree Style Tab". http://piro.sakura.ne.jp/xul/_treestyletab.html.en

At least that's the one I use.

[yellowapple]

Search DuckDuckGo for "Tree Style Tabs"; it should be the first result.

It should also be the first result if you search Mozilla's add-on marketplace thingamajig for "Tree Style Tabs". Here's the link for convenience: https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta...