We present Crossfire, a system and protocol designed to enable debugging of Web pages in another process or machine. Issues specific to any one Web browser are abstracted by the protocol and implementation, allowing a new generation of Open Web development tools to be implemented. We discuss the major refactoring of Firebug, the open source Web debugging tool to use Crossfire and the interplay between goals and resources that such an effort requires. In addition to the cross-browser focus of the protocol, we also discuss support for extensions which themselves will be cross-browser and client-server.