The reftest 1135361-ruby-justify-1.html fails on B2G, see https://tbpl.mozilla.org/?tree=Try&rev=6c37a39541ca. In the reftest analyzer images, the ruby glyphs (in both the testcase and in the reference, which doesn't use justification) look like they're placed too high relative to the base character. (Maybe this is caused by something about the metrics of the Japanese and Latin fonts that are being used in that case? If so, it might be reproducible on desktop by installing and selecting the same fonts B2G is using.)