Duplicate Tabs Closer for Chrome and Firefox is an Open Source extension/add-on capable of detecting and ultimately closing duplicate tabs.

Duplicate Tabs Closer will automatically close duplicate tabs when detected but can also be set to do nothing except monitor tabs and update the badge icon to indicate the number of duplicate tabs detected. On the remaining tab options (used with "Close tab automatically), it can do nothing (default) where nothing is done after the duplicate tab is closed. Or you can use activate once the duplicate tab is closed, the remaining tab is activated. It can also be set to apply opening tab behavior. Once the duplicate tab is closed, depending on the default tab behavior, the remaining tab will be moved to the closed tab position and activated if needed.

This will be useful for those who wind up with many open tabs where the tab's name may be obscured from view, making it difficult to decipher which tabs are duplicates.

Duplicate Tabs Closer Features:

Whitelist options (used with "Close tab automatically):
● List of URLs to not close automatically
● Duplicate tabs detected will be notified via the badge
● Wildcards are supported

Priority options (used with "Close tab automatically" mode and "Close all duplicate tabs" button):
● Keep the older tab (default): Keep the already existing tab
● Keep the older tab and reload: Keep the already existing tab and reload it
● Keep the newer tab: Keep the newer tab
● Keep tab with HTTPS (default on): Ignore the scheme part during comparison and keep the tab with the HTTPS scheme
● Keep pinned tab (default on): Keep the pinned tab

Filter options:
● Ignore case in URL (default off)
● Ignore 'www' in URL domain name (default off)
● Ignore hash part in URL (default off)
● Ignore search part in URL (default off)
● Ignore path part in URL (default off)
● Compare with title (default off)

Scope options:
● Container in the active window: only closes/displays duplicate tabs that belong to the same container in the active window
● Container in all windows: only closes/displays duplicate tabs that belong to the same container in all windows
● Active window (default): only closes/displays duplicate tabs that belong to the active window
● All windows: closes/displays duplicate tabs for all windows

Customization options:
● (only accessible from the page Options - opened from extension popup panel by clicking on the top-right icon or by opening the Extensions panel and select options)
● Duplicate tabs badge color: Set the badge color for duplicate tabs
● No duplicate tab badge color: Set the badge color for no duplicate tabs
● Show badge if no duplicate tab: Show badge with value 0 if no duplicate tabs

Similar:
● How-to Mute Tabs in Google Chrome, Mozilla Firefox, and Microsoft Edge
● Restore Accidentally Closed Browser Tabs
● How to Restore the Close All Tabs Warning in Microsoft Edge