Updates were often committed live using remote scripting (A precursor to AJAX) and we did a lot of DOM manipulation to update content in-place. At that time, we targeted IE because Netscape's support for DOM manipulation was abysmal.
While I have to give Gmail credit where it's due, I have to give Firefox the real credit for doing the hard work and finally releasing an alternative to IE that kicked JavaScript into high gear. If Gmail had never happened, it would have only been a matter of time before SPAs were going to become a thing. There were more of us doing it before Gmail than most people realize.