Various relevant docs:
Android general screen resolution/density guide:
http://developer.android.com/guide/practices/screens_support.html
CSS 3 media queries general docs:
http://www.w3.org/TR/css3-mediaqueries/
Mozilla developer network CSS 3 media queries docs:
https://developer.mozilla.org/en/CSS/Media_queries
Blog post with some details about using -webkit-device-pixel-ratio for density (note the "resolutions" in the table are sample screen pixel widths/heights, not dpi -- the density ratios are right though :)
http://www.fiveminutes.eu/targeting-hight-screen-densities-with-css-media-queries/
Sizes for iOS icons at low and high densities:
http://developer.apple.com/library/ios/#qa/qa1686/_index.html
Mac OS X resolution-independence guidelines; @2x file naming style relevant for iOS too:
http://developer.apple.com/library/mac/#documentation/UserExperience/Conceptual/HiDPIOverview/Introduction/Introduction.html
gci2014 xhdpi hdpi Retina high-resolution
See Also:
https://bugzilla.mozilla.org/show_bug.cgi?id=662169