This provides tree-style tab bar, like a folder tree of Windows Explorer. New tabs opened from links (or etc.) are automatically attached to the current tab. If you often use many many tabs, it will help your web browsing because you can understand relations of tabs.
* You can collapse/expand sub trees. It is convenient for too many tabs.
* When you close a tab which has collapsed sub tree, all of tabs in the sub tree will be closed only one action.
* The tree of tabs can be showin at rightside.
* Vertical tab bar cab be shown/hidden automatically.
* You can open new tab between existing tabs, dropping link or URL string there.
* You can save/restore the tree of tabs over sessions, by Session Manager ( https://addons.mozilla.org/firefox/addon/2324
) or other session-management addons.
* Drag and drop is available to modify relations of tabs and to rearrange. The behavior seems to be like "layer tree " of Adobe Illustrator/Photoshop.
* Tab bar can be moved to leftside, rightside, top, or bottom. Horizontal tree is also available.
* This has an API for extension authors to open child tabs for existing tabs. (See also http://piro.sakura.ne.jp/xul/_treestyletab.html.en#api
This is developed under a project to restructure TBE ( http://piro.sakura.ne.jp/xul/tabextension/index.html.en
) for Firefox 2. Multiple Tab Handler ( https://addons.mozilla.org/firefox/addon/4838
) can work with this. drag-and-do features of it will be more useful. Informational Tab ( https://addons.mozilla.org/firefox/addon/4930
) also works. With the Multiple Tab Handler, Firefox becomes like old Firefox powered by TBE.
If you don't want that Tree Style Tab automatically builds the tree of tabs, you should disable "extensions.treestyletab.autoAttachNewTabsAsChildren" by about:config. Then, you'll see tree only when you make a tree by hand, ex. drag and drop.
Pano (tree in the sidebar, based on Panorama) https://addons.mozilla.org/firefox/addon/pano/
Tab Utilities (all-in-one addon for tabbed browsing, including vertical tab bar and tab groups) https://addons.mozilla.org/firefox/addon/tab-utilities/
Tab Kit (all-in-one addon for tabbed browsing, including vertical tab bar and tree of tabs) https://addons.mozilla.org/firefox/addon/5447/
Vertical Tabs (alternative for TST + Multiple Tab Handler) https://addons.mozilla.org/firefox/addon/108862/
For developers, Tree Style Tab provides public API. By the API, you'll be able to...
* Open additional information for the current page as a "child" tab.
* Get tabs by the tree structure. For example, "parent", array of "children", next/previous "sibling", and so on.
* Collapse and expand sub tree.
* Observe changing of collapsed state of sub tree.
More information, see: http://piro.sakura.ne.jp/xul/_treestyletab.html.en#api