Comment 10 for bug 480407

There's no reverse dependency because python-xpcom isn't packaged again yet (see #352968 for the previous removal of python-xpcom). Catch-22.

See #459532 for an example of a package that requires python-xpcom. If you decide not to ship python-xpcom, you effectively make Sugar (the desktop / learning environment) unusable for the LTS as the web browser is used to download and install activities (applications) from activities.sugarlabs.org (the Sugar equivalent of addons.mozilla.org). Even more so since Ubuntu doesn't ship all of the most basic activities (e.g. Write is missing).
#364871 has another example for a package (pyjamas-desktop) breaking (indirectly via hulahop) due to python-xpcom being unavailable.