XPFE & XPToolkit permit consistent '''creation''' of user interfaces across the 3 major platforms. As for why the two names: "'XPToolkit" ' is rather synonymous with XPFE. Though the former term seems more concrete than the other, and therefore is not an exact replacement, no one is completely certain why we have both." [http://developer.mozilla.org/en/docs/Introduction_to_XUL#Terms]. From here on in we'll refer to XPFE (because it' s shorter to type). Note: This is also commonly refered to as Toolkit.  XPFE uses XUL, XBL, and RDF to achive the goal of being able to programmatlically instantiate a button (for example) using the same api no matter what platfrom you are on. XPFE uses a combination native and custom widgets to achieve the toolkit. However, from the api perspective it is platform neutral. == Sources == * [http://www.mozilla.org/xpfe/xulref/ Xul Programmers Reference]* [http://www.mozilla.org/xpfe/ The Moz Wiki XPFE page]* [http://developer.mozilla.org/en/docs/Introduction_to_XUL#TermsIntro To XUL]