.XBL File Extension
File TypeExtensible Binding Language File
What is an XBL file?
File created in the XML Binding Language (XBL) format, an XML format used to specify the presentation of .XUL user interface widgets; contains "bindings," which declare the layout of the XML interface elements; enables developers to change the look of widgets without having to modify the core functionality.
NOTE: The XBL specification was developed by the Mozilla Project and was included in many of the organization's software applications.