Just to clarify, I was using the trunk build. Specifically, Mozilla/5.0 (Windows; U; WinNT4.0; en-US; m18) Gecko/20001030.
Confirming bug on WinNT debug build 2000-10-30: the browser hangs, although Windows Task Manager never says "Not Responding", and CPU = 2%. For the record: Using trunk and MN6 branch binaries 20001030xx on WinNT, Linux, and Mac. WORKSFORME on all of these builds. WORKSFORME on Linux debug build 2000-10-30. Changing component to match bug 56355,and marking as a duplicate.
*** This bug has been marked as a duplicate of 56355 ***