This is part of the work tracked in bug 1470830. In bug 1472750, some richlistboxes that were formerly listboxes will be styled with platform styles. With "richlistbox.css" being a document stylesheet, it can now be used for styling non-anonymous children, such as the inner label created by the "appendItem" helper, leading to immediate simplification.

Screenshots: https://treeherder.mozilla.org/#/jobs?repo=try&revision=b1ab2d53f9c948f2bbb4e135c8797be4d3247f02 Baseline: https://treeherder.mozilla.org/#/jobs?repo=try&revision=37cb6189977757b617bffb87cf368d769d5ff8d3

Comment on attachment 8989945 [details] Bug 1473521 - Load "richlistbox.css" as a document stylesheet. https://reviewboard.mozilla.org/r/254954/#review262000

Pushed by paolo.mozmail@amadzone.org: https://hg.mozilla.org/integration/mozilla-inbound/rev/ba0ea459e222 Load "richlistbox.css" as a document stylesheet. r=bgrins

Backed out changeset ba0ea459e222 (bug 1473521) for bc failures in browser/extensions/formautofill/test/browser/browser_dropdown_layout.js on a CLOSED TREE Problematic push: https://treeherder.mozilla.org/#/jobs?repo=mozilla-inbound&revision=ba0ea459e2226f0ecc91f199809d5abb6a80de48&filter-resultStatus=testfailed&filter-resultStatus=busted&filter-resultStatus=exception&filter-classifiedState=unclassified Failure: https://treeherder.mozilla.org/#/jobs?repo=mozilla-inbound&filter-resultStatus=testfailed&filter-resultStatus=busted&filter-resultStatus=exception&filter-classifiedState=unclassified&selectedJob=186779426 Backout: https://treeherder.mozilla.org/#/jobs?repo=mozilla-inbound&revision=62c616e671c0dff4d47190ff1654b157f69e651d&filter-resultStatus=testfailed&filter-resultStatus=busted&filter-resultStatus=exception&filter-classifiedState=unclassified Log: https://treeherder.mozilla.org/logviewer.html#?job_id=186779675&repo=mozilla-inbound&lineNumber=8239 [task 2018-07-06T07:58:29.019Z] 07:58:29 INFO - TEST-UNEXPECTED-FAIL | browser/extensions/formautofill/test/browser/browser_dropdown_layout.js | Show one-line layout - Got true, expected false

Tests: https://treeherder.mozilla.org/#/jobs?repo=try&revision=989307820a75230191c358bd3a78681fdd01c222 Screenshots: https://treeherder.mozilla.org/#/jobs?repo=try&revision=161c73b839743912d9bd573bd65ed8d066e9eee3 Baseline: https://treeherder.mozilla.org/#/jobs?repo=try&revision=769501fbdc6b2dab9f4c9bcca66a7490063f40c7

The CSS simplifications I did some time ago for the Downloads Panel and the Downloads View made this change smaller. Note that there are two differently named lists, #downloadsRichListBox and #downloadsListBox, that are now used to select the right styling. This is slightly better than using the historical difference between class="download" and type="download", even though I kept the distinction for the rules controlling the XBL binding. In the future, we can improve the situation further and merge some styles, but I think the next step here is bug 1452629.

Comment on attachment 8989945 [details] Bug 1473521 - Load "richlistbox.css" as a document stylesheet. Redirecting review to Brian since Marco may be away, and I'd like to land this sooner.

Comment on attachment 8989945 [details] Bug 1473521 - Load "richlistbox.css" as a document stylesheet. https://reviewboard.mozilla.org/r/254954/#review262292

Pushed by paolo.mozmail@amadzone.org: https://hg.mozilla.org/integration/mozilla-inbound/rev/ff6e06d0d393 Load "richlistbox.css" as a document stylesheet. r=bgrins