Cross Platform Component Object Model (XPCOM) is a cross-platform component model from Mozilla. It is similar to Component Object Model (COM),Common Object Request Broker Architecture (CORBA) and system object model (SOM). It features multiple language bindings and interface description language (IDL) descriptions; thus programmers can plug their custom functions into the framework and connect it with other components.
The most prominent usage of XPCOM is within the Firefox web browser. Many of its internal components interact via XPCOM interfaces. Furthermore, Firefox used to allow add-ons extensive XPCOM access, but this was removed in 2017 and replaced with the less-permissive WebExtensions API.[1][2] (Two forks of Firefox still support XPCOM add-on capability: Pale Moon[3] and Basilisk.[4])