Bản dịch này chưa hoàn thành. Xin hãy giúp dịch bài viết này từ tiếng Anh.
XPCOM itself provides a set of core components and classes, e.g. file and memory management, threads, basic data structures (strings, arrays, variants), etc. The majority of XPCOM components are not part of this core set and are provided by other parts of the platform (e.g. Gecko or Necko) or by an application or even by an extension.