Tree Style Tab (TST) is widely considered the ultimate vertical tab manager for Firefox because it completely shifts how a browser handles information by organizing tabs into a visual, hierarchical tree structure. While standard browsers stack tabs horizontally or vertically in a flat list, TST automatically maps your actual browsing workflow. The Killer Feature: Automatic Parent-Child Trees
When you click a link inside a webpage, TST automatically nests the newly opened page under the original tab as a “child”.
Visual Context History: If you open five different links from a single Google search result page, those five tabs are neatly grouped and indented under the main search tab.
Collapsible Branches: You can expand or collapse entire subtrees with a single click. This means you can keep 50+ tabs open for different projects but keep your sidebar completely clean by tucking inactive projects out of sight.
Group Management: Closing, moving, discarding, or bookmarking an entire branch of related tabs takes just one click on the parent tab. Better Space Utilization