It’s using frames. The URL you bookmarked was for the frameset, which actually contains two frames - the “navigation bar” on the left, and the current content on the right.
For Netscape on the PC, right click on the portion of the display you want to bookmark, and you will get an “add bookmark” choice among other things, such as “open frame in new window”, and “view source” allowing you access to that particular frame. I imagine IE has similar functionality for dealing with frames.