I looked into why *chrome://global/skin/* doesn't seem to be applied, and I discovered that it is applied, as are other stylesheets that the platform applies by default (namely, *ua.css* and *xul.css*); but another stylesheet, B2G's *chrome://browser/content/content.css*, disables some of the default styles (like those for XUL buttons).

We should reenable those styles, and it's easy to do. Just add the following line to *prosthesis/chrome.manifest*:

    override chrome://browser/content/content.css chrome://prosthesis/content/global.css

This overrides that B2G stylesheet with our own. Note that our own stylesheet doesn't actually have to exist. Even without a stylesheet at that URL, the platform will still override the B2G stylesheet.

This change may regress B2G stylesheet rules that we want to retain. So after we do this, we'll want to watch out for those and resolve them by copying styles from the B2G stylesheet to our own. In particular, I expect that scrollbars will behave differently. But we can do that work in a separate changeset.