This came up on slashdot so I had to reply to the following comment, generating further discussion. I now understand why David and others think that Opera copied Mozilla’s features, in version 6 of Opera they introduced a SDI mode that includes a window button bar, allowing you to mix and match SDI and MDI as you wish and duplicating Mozilla’s functionality. The SDI capability is something people have wanted for years, I feel the MDI within SDI is a natural extension of Opera’s previous capabilities, obviously others feel differently or don’t realize Opera has had the window bar since version 4.
I was browsing David Hyatt’sblog (he’s a Mozilla hacker) and noticed that he claims that “Opera only added tabs in its newest version after Mozilla had them already in its trunk builds.”
Opera introduced its ‘Window Bar’ with Opera 4, wich came out in spring of 2000. Around that time Mozilla was at M14 and the first Netscape 6 Preview was being released. Neither of those had the equivalent to Opera’s Window Bar. The first mention of Mozilla ‘tabbed browsing’ I can find is a year later, contained in this post to the Mozilla newsgroups. Implementation didn’t happen until late summer or fall of 2001, possibly being beat to it by the Multizilla project.
Of course NetCaptor had it back in ’99, maybe even earlier…