Once we have a developer mode in the desktop runtime (bug 899656), we should build the Firefox developer tools directly into the runtime, so users can access the tools in the same window as their app instead of having to use the remote developer tools in Firefox, which requires them to repeatedly switch windows to go between their app and the tools. Some of the developer tools code is already in toolkit/, but other code is in browser/ and assumes it is being loaded in a Firefox browser window, so it would have to be modified to work inside non-Firefox windows, and it may have to be refactored into toolkit/ (or another directory shared between the browser and the runtime). We've talked about doing this for the Simulator, which is similarly a XUL app whose main window contains a content frame, so presumably the same refactoring could be used by both projects.

Per bug 1238079, we're going to disable the desktop web runtime and remove it from the codebase, so we won't fix these bugs in it.