Actually, Opera was the one to invent tabs. Does someone remember why Firefox took off while Opera never managed to come out of its niches?
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.