User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.75 Safari/537.36 Steps to reproduce: 1. goto about:config 2. messing around with gfx.font_rendering.cleartype_params.rendering_mode 3. every rendering mode listed on msdn (http://msdn.microsoft.com/en-us/library/dd368118.aspx) could be set except for DWRITE_RENDERING_MODE_OUTLINE Actual results: Jonathan Kew (:jfkthame) explained why this mode was left out 5 years ago in bug 642589: https://bugzilla.mozilla.org/show_bug.cgi?id=642589#c53 But he left no detail about what didn't work so I couldn't test myself, but with the extenson "AA tuner (https://addons.mozilla.org/en-US/firefox/addon/anti-aliasing-tuner/)" I can use DWRITE_RENDERING_MODE_OUTLINE on every site I visit without seeing any visual glitches or display problem. Maybe something caused Jonathan's problem 5 years ago has now been fixed? DWRITE_RENDERING_MODE_OUTLINE should be available as any other rendering modes does since it can provide the best rendering result for CJK characters among all rendering modes (non-CJK characters will also benefit), especially on today's high-density devices. It's been missing for 5 whole years! Maybe it wasn't that important back then, but clearly high-density devices are becoming mainstream, shouldn't this be reconsidered? Expected results: when gfx.font_rendering.cleartype_params.rendering_mode is set to "6", rendering mode "DWRITE_RENDERING_MODE_OUTLINE" would be used.