Netscape's vision was java applets though, right? The only thing I can remember that was worse in a browser than Flash. Perhaps we owe Microsoft some thanks.
XMLHTTP was originally an ActiveX technology, though, from the Outlook team; it wasn't originally developed as part of IE. I guess it wasn't until Mozilla and Apple added a native version that it really took off.
Actually KHTML and Safari supported it earlier, MozillaSuite/Firefox initial support was broken and only when it was fixed in Firefox around 2004 it got tradtion among devs.