Luxilla is a runtime/browser that turns XUL (XML User Interface Language) into live windows, dialogs, menus, toolbars and more without requiring a single-line of Java code. Pass on the chrome folder holding your XUL markup and see it come alive.
This has a Python ICAP (Internet Content Adaptation Protocol) server and IRML parser. Using this, a web proxy can do rule-based adaptation of content before delivery to clients. Has a Python proxylet API and squid-icap-client code too.