Chrome-only appearance properties break when a style from chrome://global/skin/in-content/ is included

[aubymori]

Whenever a stylesheet from chrome://global/skin/in-content/ is included, appearance properties that are limited to chrome/UA stylesheets (menupopup, menuitem, groupbox, etc.) break across all stylesheets. This is most notable in about:config, where the inclusion of chrome://global/skin/in-content/info-pages.css breaks the menupopup styles defined in chrome://global/skin/global.css.

With in-content stylesheet:

Without:

This happens with both xml-stylesheet and html:link[rel="stylesheet"]. It should also be noted that removing the in-content stylesheet with the developer tools while the page is loaded does not affect the appearance properties, unless a new stylesheet that defines them is added then after. Basically, this affects the page load.