Latest Windows 11 added tabs in Explorer. It's not yet pushed to all users but should be easy to detect (and it's coming to everybody later this month, anyway)
In Firefox downloads, the "Show in Folder" button opens a new explorer instance.
If it's possible, detect user's Windows version and have a flag in options that forces the folder to open in a new Explorer tab instead, if there's at least one Explorer instance running. If there's none, launch an instance like normal and in case there's more than one, enumerate and pick the first.
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