Tree Style Tab

During research the tabs keep multiplying until the tab bar is a row of favicons, you can't remember which page opened which, and closing a whole group of related pages means hunting them down one by one.

Tree Style Tab moves Firefox's tabs into a sidebar and arranges them as a tree by how they were opened: a tab opened from a page nests under it, so each topic naturally forms a group you can collapse, drag or close together. Full titles stay readable in the sidebar no matter how many tabs you have.

It's one of the most popular tab managers for Firefox, free and open source, used daily by well over a hundred thousand people.

Features

Tree of tabs: new tabs become children of the page that opened them, making relationships obvious.

Collapse and group actions: collapse, expand, move, close or bookmark an entire subtree.

Drag and drop: drag tabs to change their nesting and order.

Vertical sidebar: full titles in a sidebar on the left or right, more useful than a top tab bar on wide screens.

Themes: built-in Photon, Proton, Sidebar and High Contrast themes, plus custom CSS.

Native-like menus: the tab context menu matches Firefox's own, and long-pressing the new tab button picks a container.