Mozilla refuses to work with a number of technically invalid JavaScript constructs, which are in common use in the wild because they were implemented in Netscape 4.x or IE. For Mozilla, this makes perfect sense. 'Encouraging' standards-compliance is a good thing. However, if we want to ship Mozilla as a replacement for Netscape, perhaps we should be slightly more permissive. I don't know how feasible it is to support the non-standard extensions such as the ones used by https://www.nwolb.co.uk/ but I think it's going to be quite a long time before server admins catch up and make it work. If it's feasible to make these sites work for users of Red Hat's Mozilla, by implementing backward-compatibility with Netscape 4.x, then it will make the migration from Netscape far easier.
This bug is too vague. The javascript error in this case was: netscape.softupdate has no properties. I'm not sure if that's a bug or not. :) It should end up in mozilla's bug repository if it actually is a bug, though.
You could perhaps make a case for forgiving the lack of netscape.softupdate. If you're so inclined, ignore the softupdate bit and go directly to the login page. cf. Mozilla bug #65944.