It is most likely a particular website that is causing IBrowse to crash. When IBrowse crashes, if you try to load the same site after a reboot, and it still crashes, then obviously that would confirm it. AFAIK, IB2.4 will be crash free - there are almost too many bugfixes to count.
However, how many connections have you told IBrowse to use? This is important because you mention MiamiDx and ADSL. MiamiDx (and Miami) actually have a nasty bug which causes incoming data to be corrupted under heavy network loading, which will happen if you set the number of connections too high. That said, this usually doesn't lead to crashes, but visually corrupt images being rendering on webpages.
I should also add that stack size is not the issue here.