Venkman was built into the Mozilla Suite [1], and it was also made into an addon for Firefox [2] when Firefox was released.
DOMi was built into Firefox since November 2003 if you used the Windows installer's 'Custom' installation and selected the checkbox for inclusion [3], then in Firefox 3 it was removed and made available as an extension [4]. It was also included in the 'Custom' installation of the 'Complete' Mozilla/Seamonkey Suite [3].
But Prototype.js came out in 2005, jQuery in 2006. Ajax the term was coined in 2005 [5][6][7]. We don't talk about the dark days before then.