STR:

1. Go to https://www.moneysmart.gov.au/investing/financial-advice/financial-advice-toolkit.
2. Mouse over the numbered items with the purple circles.
3. Notice that on mouse over the purple circle disappears, and after mousing out it doesn't reappear.

Expected results:

The background changes on hover and the purple circle doesn't disappear.

12:17.32 INFO: Last good revision: dfefd2d4d63f8f2cdeb57e6ee16a8c31c4f54447
12:17.32 INFO: First bad revision: 6b71e3d434c232998629b8e18a983212e9d3fc9d
12:17.32 INFO: Pushlog:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=dfefd2d4d63f8f2cdeb57e6ee16a8c31c4f54447&tochange=6b71e3d434c232998629b8e18a983212e9d3fc9d

Looks like it's bug 1525134. Emilio, do you have time to take a look?

.accordion-subSection h4:not(.noCircle)::first-letter {
    color: #ffffff;
    font-size: 1.5em;
    width: 1.4em;
    overflow: auto;
    display: inline-block;
    text-align: center;
    vertical-align: middle;
    margin-right: 0.5em;
    padding: 0.2em 0.5em;
    background: url("/media/559754/circle-6d3a96.svg") 0 0 no-repeat;
    background-size: contain;

}

This is more consistent with all the other image request code, and handles
pseudo-elements properly without having to add more out-of-band calls to
UpdateStyleOfOwnedChildFrame and such.

So that the continuation pointer is setup before DidSetStyleContext runs.

I don't see any reason for not doing this, the current thing is a footgun.

Backed out changeset d33544f0d8e6 (bug 1528451) for Assertion failure: IsResolved ...nsStyleStruct.h failures

push that caused the backout: https://hg.mozilla.org/integration/autoland/rev/d33544f0d8e6197126399ad928adc701582d947a

failures: https://treeherder.mozilla.org/#/jobs?repo=autoland&resultStatus=testfailed%2Cbusted%2Cexception&classifiedState=unclassified&selectedJob=229167386&searchStr=windows%2C7%2Cdebug%2Cmochitests%2Cwith%2Ce10s%2Ctest-windows7-32%2Fdebug-mochitest-browser-chrome-e10s-2%2Cm-e10s%28bc2%29

backout: https://hg.mozilla.org/integration/autoland/rev/4af3691edfe75e542eb362b674cdfcc3aa5a81c8

There was a XUL subclass that only gets images on windows, which was not calling the base class' DidSetComputedStyle function.

https://hg.mozilla.org/mozilla-central/rev/2bbbcf59d8f9