In fact Opera were more ahead of their times, because they were the first to add tabs and had a lot of features that we now take for granted. I know this because I used Netscape browser (before they were called mozilla) and Opera 4.x at the time.
Opera were visionary. But I was only referring to detached tabs, which Mozilla implemented, Chrome followed and now Vivaldi.
What are detached tabs? Sandboxed? Dragged out into their own window? Genuine question