In Firefox25, Mozilla added a couple scary media queries
(-moz-os-version and -moz-osx-font-smoothing).
I think we should get rid of these, as well as most/all of the prefixed
media queries in
​https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Media_queries#-moz-os-version.
Either just disable them, or make them lie.