I think he perhaps means tabs with a true document interface[1] (i.e multiple web pages can be opened within the same application window and be resized, moved, tiled, and cascaded like normal application windows in the operating system).

Edit: Seems Opera added tabs slightly before Mozilla after looking it up out of interest[2]. Also just some random history on tab integration in web browsers. Mozilla 0.9.5 added them a few months after Opera 4 in 2001, though of course neither was the first. I guess one can say Opera was the first browser to add them that is still a fairly popular browser in present day.

Four years later, in 1994, BookLink Technologies featured tabbed windows in its InternetWorks browser. That same year, a text editor called UltraEdit also appeared with a modern multi-row tabbed interface. The tabbed interface approach was then followed by the Internet Explorer shell NetCaptor in 1997. These were followed by a number of others like IBrowse in 1999, and Opera in [June] 2000 (with the release of version 4 - although a MDI interface was supported before then), MultiViews October 2000, which changed its name into MultiZilla on 1 April 2001 (an extension for the Mozilla Application Suite[7]), Galeon in early 2001, Mozilla 0.9.5 in October 2001, Phoenix 0.1 (now Mozilla Firefox) in October 2002, Konqueror 3.1 in January 2003, and Safari in 2003. With the release of Internet Explorer 7 in 2006, all major web browsers featured a tabbed interface.

[1] http://en.wikipedia.org/wiki/Features_of_the_Opera_web_brows...

[2] http://en.wikipedia.org/wiki/Tabbed_browsing#History

I have tried to find said discussion in vain. It's more about the attitude of Firefox users against Opera than anything else.

That big ad is a sad bit of Internet history. A wasted opportunity.

Also: they had a deal with Google to make it the default search engine before Firefox had one.