Based on Mozilla bugs 1119128, 1285533, and 1421964.
gfx.font_rendering.fontconfig.fontlist.enabled is no longer available.
gfxFontconfigUtils.h still exists, and will be removed in another commit. Just
need more research on bug 1385029.
Tag #1862
ScrollbarStyles contains values of overflow, (over)scroll-behavior, etc.
The only one which is marginally related to scroll _bars_ is overflow, which can
be used to hide scrollbar (by making an element not scrollable) or enforce the
scrollbar to display.
It makes more sense to be called ScrollStyles as it's mainly concerning behavior
of scrolling, not scrollbars. Also, with the addition of scrollbar width
properties, the current name can be confusing.
This make MediaQueryList inherit from EventTarget and adds MediaQueryListEvent
as an interface as well as the onchange() method.
This should not affect compatibility with other code; the event object is a
MediaQueryListEvent instance, which is recognized as a MediaListQuery instance.