The most crufty part in both mozilla's code base and libreoffice code base is essentially equivalent in that it tries to solve essentially same set of problems (cross-platform UI and object model), but the implementation is significantly different, because in mozilla's case this layer of cruft was introduced 20-ish years ago as a complete rewrite of the thing (and most of the really ugly hacks have to do with sub-par C++ compilers and support for classic MacOS), while there was no attempt at a major rewrite of the staroffice codebase until libreoffice (and it is quite obvious that the way libreoffice's rewrite proceeds is at least partially motivated by experience from how the netscape->mozilla rewrite suffered heavily from second system effect and in the end failed at least from the bussines standpoint).