Have a look at the main UI, should be self explanatory: https://upload.wikimedia.org/wikipedia/en/6/6f/Opera_7.02.pn...
And on top of that it was skinnable and customizable to a degree no other browser has matched since.
Opera introduced the banner after Mozilla was formed and started offering first a rewritten Netscape package (these days called Seamonkey) and then Firefox (after some back and forth about naming).
Need to research and compare a bunch of sites at once? Throw the tabs into a window of their own and tell the window to tile the tabs.
One of the reasons i still stick with Opera 12.