Tab Deduplicator от jplayer01

The add-on behaves differently depending on the current state:
- If you left click a link which is already open in a different tab, that tab will be activated and set to the focused tab. A notification will be shown informing the user of this change, which can be clicked to return to the previous tab.
- If you click on a link with the middle mouse button, no new tab will be created if an existing tab with that link is found. A notification will be shown which can be clicked to switch to the existing tab. You can also switch to the existing tab by holding shift when you middle mouse click the link (or simply left clicking the link).
- If you enter a URL into the address bar, it will switch to an existing tab with that URL if one is found. The previous tab will be closed (due to limitations with the WebExtensions API).

Limitations:
- Once you load a new page after clicking a link, the URL might be changed on some sites (like Amazon), particularly due to URL tracking. Since the final URL differs from the original link you clicked, the add-on won't be able to detect and prevent duplicate tabs being opened with that link.