Our HiDPI support on OS X (Retina) is pretty decent, and so as a first step for our Windows HiDPI support we should get it up to parity with that. Patches from existing bugs can serve as a template (mainly bug 781327 and bug 817366). Roughly this work covers: - main icon sheet (Toolbar.png) - Australis tabs and Customization UI - doorhanger icons - identity/ssl indicators - media controls - arrowpanel arrow - lots of random icons and tiny widgety glyphs Note that there will soon be ongoing work in the deps of bug 1016548 ("Finish OS X HiDPI support for Firefox front-end"), and so in a few cases there is a bit of overlap because the current OS X implementation is incomplete. Also note that we need to figure out the implementation plan for HiDPI on Windows (bug 1023488) before diving into this work.