1980346 - Duplicate Taskbar Tab is created when trying to launch a pinned Taskbar Tab if taskbartabs.json file is deleted

Status: NEW

(Firefox :: Web Apps, defect, P3)

Description

[Alex Cornestean]

Attachment: 2025-07-30_10h57_15.mp4

Affected Version:
Nightly - 143.0a1/20250730213201
Beta – 142.0b5/20250730090632

Description:
Trying to launch a Taskbar Tab pinned to the taskbar when the main Firefox instance is closed and the taskbartabs.json file from the profile folder is deleted will cause a duplicate Taskbar Tab to be created and be launched. The original pinned shortcut will become inactive and not launch a Taskbar Tab window.
Additionally, the second Taskbar Tab that is created will have a different icon compared to the original Taskbar Tab.
If the taskbartabs.json file is left as is and not deleted, the issue will not occur.

See attached video for more details.

Step to reproduce:

1. Launch Firefox with a new profile
2. Access about:profiles and identify the in-use profile. Click the “Open Folder” button of the “Root Directory” row of the profile entry to open the profile folder and set it aside for later use
3. Enable Taskbar Tabs via browser.taskbarTabs.enabled in about:config and restart the browser
4. Access https://www.wikipedia.org/ and click the pageAction to create a Taskbar Tab
5. Pin the Taskbar Tab to the taskbar when prompted
6. Close the Taskbar Tab and the main Firefox instance
7. In the profile folder window from Step (2), locate the taskbartabs folder (a refresh might be needed for the folder to show up since the window was opened beforehand)
8. Delete the taskbartabs.json file from the taskbartabs folder
9. Click the pinned Taskbar Tab on the taskbar to launch it
10. Notice the original Taskbar Tab does not launch, but instead a duplicate Taskbar Tab is created
11. Pin the newly created Taskbar Tab and notice its icon is different from the original Taskbar Tab
12. Click the original Taskbar Tab again and notice a new window for the second Taskbar Tab is opened i.e. the original Taskbar Tab is inactive

NOTE:
The issue does not occur if the same steps are performed but the taskbartabs.json file is not deleted. For this:

1. Return the second Taskbar Tab to the main Firefox instance via the pageAction. This will cause the second Taskbar Tab to be unpinned and the main Firefox instance to launch
2. Unpin the original/first Taskbar Tabs from the taskbar
3. Create a new Taskbar Tab from the one returned in Step (1) via the pageAction and pin it to the taskbar
4. Close the main Firefox instance and the newly created Taskbar Tab
5. Click the pinned Taskbar Tab on the taskbar to launch it
6. Notice that the Taskbar Tab is properly launched and a secondary Taskbar Tab is not created

Actual results:

1. A duplicate Taskbar Tab is created when trying to launch a pinned Taskbar Tab if taskbartabs.json file is deleted beforehand.
2. The original Taskbar Tab becomes inactive
3. The second Taskbar Tab has a different icon compared to the original Taskbar Tab

Expected:
The original pinned Taskbar Tab should launch even when the taskbartabs.json file is deleted.