You can modify the Firefox desktop shortcut to add a modified target path to force the browser to always launch in private browsing mode.

To modify the Firefox desktop shortcut file path:

1. Press the Win key and type Firefox. Right-click on the Firefox icon and select Open File Location.
   

   

2. Next, right-click on the Firefox icon in File Explorer and select Show More options.
   

   

3. In the Classic context menu, select Send > Desktop (create shortcut).
4. Right-click on the newly created Firefox desktop shortcut and select Properties.
5. In the Properties dialog, open the Shortcut tab.
   

   

6. In the Target field, add -private-window at the end of the existing file path.
   “C:\Program Files\MozillaFirefox\firefox.exe” -private-window
7. Click OK to save the changes. Click Continue to give administrator permission in the Access Denied dialog.

Rename the modified Firefox shortcut for easier distinction between the regular and the incognito browser shortcut. Double-click on the new shortcut to launch Firefox in incognito mode.