We added support for -webkit-min-device-pixel-ratio a while back, but we had to turn it off because it broke Google Docs -- bug 1237101. (It didn't break due to a flaw in the feature, but rather because Google Docs used a -webkit-min-device-pixel-ratio media-query to control some CSS that required another basically-unrelated CSS feature to work correctly -- 'content' on non-pseudo-elements. See bug 1237101 comment 6 for more.) Happily, it seems Google Docs has changed such that it no longer depends on this usage of 'content' on non-pseudo-elements! (at least, not in a way that causes visible breakage - see bug 1237101 comment 25 - 26) So, let's try turning -webkit-min-device-pixel-ratio support back on. I intend to land a patch for this (just a pref flip) around the beginning of the Nightly 61 cycle.

BTW: this feature has been (& is still) tested, via this chunk of "test_media_queries.html": > test_device_pixel_ratio("-webkit-device-pixel-ratio", > "-webkit-min-device-pixel-ratio", > "-webkit-max-device-pixel-ratio"); https://dxr.mozilla.org/mozilla-central/rev/a6f5fb18e6bcc9bffe4a0209a22d8a25510936be/layout/style/test/test_media_queries.html#452 ...combined with the fact that we've kept this feature enabled for mochitests: > user_pref("layout.css.prefixes.device-pixel-ratio-webkit", true); https://dxr.mozilla.org/mozilla-central/rev/a6f5fb18e6bcc9bffe4a0209a22d8a25510936be/testing/profiles/prefs_general.js#184-185

In case it's helpful for review purposes, here's the commit where we simultaneously added this pref & turned off this feature (in bug 1237720): https://hg.mozilla.org/mozilla-central/rev/be92e1923730

Comment on attachment 8958201 [details] Bug 1444139: Re-enable support for webkit-prefixed pixel-density media queries (e.g. -webkit-min-device-pixel-ratio) https://reviewboard.mozilla.org/r/227136/#review233062

Pushed by dholbert@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/3187e7424f01 Re-enable support for webkit-prefixed pixel-density media queries (e.g. -webkit-min-device-pixel-ratio) r=xidorn

cpeterson says this seems to have regressed Google Docs for him. :-/ So it seems bug 1239922 isn't fixed after all, and we can't ship this pref-flip yet. I'll back out.

Backed out: https://hg.mozilla.org/integration/mozilla-inbound/rev/ddf403e7832f1bfbf72e4fcb8fee051ccf89e712

(In reply to Daniel Holbert [:dholbert] (away 4/24 - 5/11) from comment #8) > cpeterson says this seems to have regressed Google Docs for him. :-/ So it > seems bug 1239922 isn't fixed after all, and we can't ship this pref-flip > yet. > > I'll back out. Gah, I missed this. Thanks Daniel. Here's Chris' description of the issue: https://bugzilla.mozilla.org/show_bug.cgi?id=1239922#c13

We might be able to try this again, now that bug 215083 is fixed!

Yup, I think we can. In a build from 2018-06-29 (before bug 215083 landed), I still see issues like bug 1239922 comment 13 when I enable this pixel-ratio pref. But in a build after that (tested 2018-07-01 and today's nightly), I do not see any such issues.

Note that this pref now lives in a different file, per bug 1448225. I'm updating the patch to tweak the value in that new location - still a one-liner s/false/true/ sort of change, so I don't think re-review is needed.

Pushed by dholbert@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/7d3fe27beec5 Re-enable support for webkit-prefixed pixel-density media queries (e.g. -webkit-min-device-pixel-ratio) r=xidorn

Hi Daniel, can I just check — this is enabled for 63, but is that just on Nightly, or across all versions?

Hi Chris! This doesn't have any sort of nightly-only guard -- it's enabled for all categories of releases, and is riding the trains with 63.

(In reply to Daniel Holbert [:dholbert] from comment #18) > Hi Chris! This doesn't have any sort of nightly-only guard -- it's enabled > for all categories of releases, and is riding the trains with 63. Ah, super — thank you.