Duplicate tabs i.e. the same URL opened in more than one tab clutter your browser window unnecessarily. Duplicate tabs are mostly opened by accident or forgetfulness, and rarely out of necessity. We tend to open some of our most frequently used sites multiple times because we forget we already have them open in a different tab, or we can’t find them. LinksWatched is a Firefox add-on that helps fix both these problems; it alerts you when you open a duplicate tab by adding a red border inside the window when a duplicate link is opened, and giving you a desktop notification alerting you that you’ve opened a link that’s already open in another tab, with the option to switch to it. Compared to extensions like Prevent Duplicate Tabs for Chrome that just close the duplicate tab, LinksWatched doesn’t dictate what is done with the duplicate tabs, so the control stays with you.
Once you’ve installed LinksWatched, you can continue browsing like normal since there isn’t anything to configure. Whenever you click a link and it’s already open in some other tab, a red border will appear within the window frame, even if the tab is in another window. The border appears only after the page has finished loading, and remains visible as long as a duplicate tab is open.
A desktop notification alerts you about the duplication and provides you with a link to close the new duplicate tab and switch to the one that you had opened first.
LinksWatched works great and I like it better than Prevent Duplicate Tabs because the duplicate tab isn’t automatically closed for me. The add-on recognizes that at times, you really do need to open the same page in multiple tabs. There are two things that need fixing though: first, when the link in the notification is clicked after the window that the other tab is open has been minimized, it will not be maximized/restored. The relevant tab will still be selected so that when you manually restore the window, you see the tab, but this is practical only if you have two windows open and can safely assume that the other tab must be open in the second window. With multiple windows open, you get no indication about which window has that tab.
Secondly, the add-on doesn’t identify a duplicate tab until the page has finished loading. This might be because it’s waiting for the page to perhaps load a script or query that might navigate to a different URL, but this results in the add-on taking its time to detect the page as a possible duplicate. If you open a duplicate tab in the background, the notification is the only thing that will alert you unless you switch to the tab itself.