One of the sub-tests of dtls-2.html is failing with some patches I'm writing for stylo. I think there might be an issue with the underlying feature rather than with my patches. Here's a reduced/modified version of that test: https://people-mozilla.org/~cmccormack/dtls/dtls-2.html When the document is loaded, you see four square glyphs. After five seconds, the style="" attribute of the <mstyle> element is modified, removing the font-feature-settings property. At that point, you see square, triangle, square, triangle. If you then open the devtools, the second square turns into a triangle. I guess this is not expected, but I don't really know where the problem lies. Maybe we end up reflowing and the text runs end up shaping the text differently? In any case, I'm going to mark the test as expected-failing for stylo when I land my patches (I'm not sure if it's bug 1289868 or bug 1364845 that reveals the problem), but it would be nice to know what's going on here. CCing a few people who might know.