Well, like the comment said, it crashed a lot when you tried to run JS on it. It was pretty annoying to binary-search for a bug in your JS when the symptom was a browser crash. Also, it used a lot more RAM than Netscape 3 and was slower, but I don't recall it being better in significant ways.
DHTML in Netscape 4 was also completely incompatible with DHTML in IE 4. In IE you had the DOM, which is an inconvenient and inherently very inefficient interface that you could coerce into doing anything you wanted. In Netscape 4 you had layers. Our team (KnowNow) was working on an AJAX and Comet toolkit at the time (02000). In order to not write separate versions of our Comet applications for the two browsers, we stuck to the least common denominator, which was basically framesets and document.write.
reconnecting
Indeed, browsers learned how to hurt people from their earliest days.
DHTML in Netscape 4 was also completely incompatible with DHTML in IE 4. In IE you had the DOM, which is an inconvenient and inherently very inefficient interface that you could coerce into doing anything you wanted. In Netscape 4 you had layers. Our team (KnowNow) was working on an AJAX and Comet toolkit at the time (02000). In order to not write separate versions of our Comet applications for the two browsers, we stuck to the least common denominator, which was basically framesets and document.write.