From vague memories I remember NN4 on classic MacOS was, I recall, a total memory leaking / crashing shitshow. I worked in a shop that had a bunch of Macs and the rule was you couldn't run FileMaker (which they used a lot) and Netscape at the same time because the two would just run over each other memories. The glory days of lack of memory protection on MacOS 7.6.

But I also don't think 3 was much better.