I imagine this has a similar route cause as to bug 1406134. The quick and dirty fix would be to do what we did (temporarily, although I have no found the time to work on this as of yet) for moz-page-thumb, i.e.: https://searchfox.org/mozilla-central/rev/b9da45f63cb567244933c77b2c7e827a057d3f9b/image/imgLoader.cpp#2104
Bug 1548835 Comment 6 Edit History
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I imagine this has a similar root cause as to bug 1406134. The quick and dirty fix would be to do what we did (temporarily, although I have no found the time to work on this as of yet) for moz-page-thumb, i.e.: https://searchfox.org/mozilla-central/rev/b9da45f63cb567244933c77b2c7e827a057d3f9b/image/imgLoader.cpp#2104