If they really want a history lesson, then return to the pre-browser days -- yeah, you had to #ifdef and port your code over and over and over, always chasing the latest APIs (the time of origin of that horrible phrase, in fact).
Standardization fixed that.
Apparently you weren't doing web development back in the Netscape 4.7 days. :)
IE 5.5 and 6 were actually big steps forward for web standards back in 2000-2001. They were actually decent browsers then. Not perfect, but no one was. The problem isn't IE6 - it's that Microsoft stopped with IE6 for such a long time.
Tabs were the last thing that struck me as innovative. I was hoping Google's sidebar idea would take off but it doesn't seem terribly popular. I wish the social internet (not so much facebook, but discussion forums like this or persistent comment communities) were decoupled from content, such that commentary was not siloed on the same page as the content.