Opera and Firefox, "actually" (along with some lesser-known browsers), introduced tabs around the same time as, or very soon after, the launch of Windows 2000.

Alternatively, read "tabs" as "windows" - we know the word "tabs" is not the important point of that post (and that the number 200 is exaggerating for effect). Right clicking a link and selecting "open in new window" opened a new window in the same browser instance, not a separate instance, although there wouldn't be any visual difference.

Windows XP and Windows Server 2003 were the current versions at the time.