Free marketing, by every linux advocate ever. Chrome overtook in a similar manner, by getting free marketing on Google.com.

Have a look at the main UI, should be self explanatory: https://upload.wikimedia.org/wikipedia/en/6/6f/Opera_7.02.pn...

Except it looked like this when it came out with tabs: http://i.imgur.com/ms0RsfB.png

And on top of that it was skinnable and customizable to a degree no other browser has matched since.

Until they dropped it with the transition to a Chromium base, the "tabs" in Opera was full blown MDI.

Yep, and it is awesome.

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.

Did you really not see the gigantic banner ad in the middle of the main UI? Opera tried to monetize the browser in that way for years.

Much like Android apps that offers a choice between ads and paying to make them go away. Opera was initially for pay only, much like Netscape Navigator. IE was the really odd one out by being offered for free (and why Netscape pulled Microsoft to court over antitrust charges).

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).

For one thing it's not open source and never was.