Google AdWords Editor is a cross-platform application powered by Mozilla's XUL technology stack. We build upstream Mozilla code into a XUL application container called xulrunner.

Since we are compiling the source code ourselves, rather than using a compiled xulrunner prepackaged by a third party, we are obliged to make it clear exactly what source we are compiling, and to make our small set of modifications to Mozilla source code available to anyone who downloads AdWords Editor. You can find information on all of this here.