Open Tabs
There's a view called "Open Tabs" which lists all your open tabs, either in the current window only or, if unchecked, in all open windows of your browser.
Experimental
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Click this icon to access the "Open Tabs" view
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If you cannot see this icon, you might have to enable the "open tabs" feature in the settings.
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Tabs with grey background are already stored in a tabset; the yellowish background indicates that we have duplicate tabs.