About this extension

This extension provides the ability to work with tabs as "trees".

New tabs opened from the current tab are automatically organized as "children" of the current tab.
Such "branches" are easily folded (collapsed) by clicking on the arrow shown in the "parent" tab, so you no longer need to suffer from too many visible tabs.
If you want, you can restructure the tree via drag and drop.

Such a tree of tabs will behave like a visual browsing history for you.
- For example, if you see a list of search results for a topic, each search result link will open in new child tab.
- New tabs opened from these "child" tabs will appear as descendants of their originating tabs.
- You'll easily dig and dig deeply, without losing your browsing trail - if you want to go back to the original search result, you just have to switch to the "root" tab.
Moreover, each tree will reflect a group of tabs on a similar topic.

Please enjoy as you like!

Tips:

"F1" key toggles the TST sidebar.
"Tree Style Tab" toolbar button also toggles the sidebar. If it's unnecessary, you can remove it from the toolbar.

Permissions:

This extension needs following permissions to work as expected:

Required:
- Access browser tabs: to list both active and non-active tabs in the UI.
- Access recently closed tabs (access to the session information): to save tree information of tabs (structure, collapsed/expanded state, etc.) to tabs' session information and ask to Firefox to manage them as bundled.
- Display notifications to you: to present information and navigate users without blocking.
Optional:
- Read and modify bookmarks: to simulate bookmark related commands in the tab context menu. / to detect tabs whether they were opened from bookmarks or not.
- Access your data for all websites (run scripts on webpages): to detect the Ctrl key is pressed/released and prevent needless expansion of collapsed trees while tab switching with Ctrl-Tab/Ctrl-Shift-Tab.
- Hide and show browser tabs: just for automated tests, not required on regular use.

Extensions extend TST:

TST provides APIs for other extensions.
Some extemsopms extend the behavior of TST's sidebar panel:

Multiple Tab Handler allows you to select multiple tabs with long-press on tabs. It also allows you to close mutiple tabs with long-press on the closebox on tabs.
TST Active Tab in Collapsed Tree shows a small tab on a collapsed tree as an alias for the last active tab under the tree.
TST Auto Group Tabs provides ability to group newly opened tabs automatically in various conditions.
TST Auto Sticky Tabs provides ability to stick some state tabs to tab bar edges automatically.
TST Bookmarks Subpanel allows you to show a small "Bookmarks" sidebar panel below tabs in the TST's sidebar.
TST Lock Tree Collapsed allows you to lock arbitrary trees as collapsed. (This was a built-in feature on TST 3.3.0-3.3.6, and now separated.)
TST Indent Line provides indent lines like Visual Studio Code's one.

And there are more helper extensions.

Developer comments

## Similar projects

*Tree Tabs:
Cross-browser, more powerful features, and high customizability.
(One large difference between TST is: the design strategy.
TST is aimed to keep it simple and work together with other addons as possible as it can.)
*Sidebery:
Another tree addon with powerful features.
* Tab Center Reborn:
Vertical tab bar without tree.
* sidebarTabs:
Vertical tab bar with grouped tabs.

There are more similar projects by someone not me, for Firefox or Chrome. Please try them if TST does not perform as you expected.

## Public API for other addons

For addon authors, Tree Style Tab provides public API. If your addon provides extra context menu items for context menu on tabs, you can easily support TST's context menu with small changes. For more details, see the API document.

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Release notes for 4.2.3

4.2.3 (2025.6.23)

Context menu commands now works even if it is opened on a blank space (by joanbm. Thanks!)
Add an expert option to activate/deactivate native tab groups management UI (corresponding browser.tabs.groups.enabled of Firefox itself).
Scroll pinned tabs container when an out-of-view pinned tab become active.
Remove dragged tabs from their group when they are dropped before a group header explicitly.
Don't create needless new group when a last member is dropped before the next another group but the tab is not moved actually.
Disallow to resize pinned tabs area size larger than required.
Unblock user operations correctly after drag-and-drop of tabs across windows. (regression at 4.2.0)
Treat focused or active tab as the context tab if the context menu is opened via the keyboard (ex. Shift-F10 on Windows).
Accept more cases of dropped native tabs.
Delete obsolete option to deactivate using of tab multiselection API.

4.2.2 (2025.6.9)

Pinned tabs are rendered with expected position after rearranging by drag-and-drop. (regression at 4.2.0)
Apply designed colors always for the "Sidebar" skin, even if the "Dark" color scheme is active. (regression at 4.2.0)

4.2.1 (2025.6.7)

Scroll to the active tab correctly with disabled animation mode. (regression at 4.2.0)
Detect sidebar position automatically even if the window is in a screen placed leftside of the primary screen.
Scroll to the new active tab and keep it in the viewport more correctly even if there are going-to-be-collapsed and/or sticky tabs.
API: a scroll type message now accepts a new parameter group to scroll the tab bar to the specified tab group.

4.2.0 (2025.6.2)

Drop support of Firefox older than 139.
Add support of native tab groups feature of Firefox itself. TST will create a new tab group of Firefox itself instead of modifying tree, when you drag a tab to the head side edge of another tab.
Show muted state indicator and sharing state indicator (for microphone, camera and screen) at the position same to the one on Firefox's native tab.
API: Some notification type messages (ex. tab-mousedown) can contain Firefox's tab groups as a tab (tree item). They have properties similar to regular tabs but there is one difference: they have "group" as the value of their type property.

Tree Style Tab by Piro (piro_or)

Required permissions:

Optional permissions:

Used by

Required permissions:

Optional permissions: