Reading the notes in comment 0 here... I wonder if the "Delay dispatching threads" / "Delay task running" items there might cause **particular slowness for style-system tests**, since our style system is multi-threaded. That would explain why `outline-valid-mandatory.html`'s seemingly-benign calls to `test_valid_value()` (which resolves some CSS) would end up being 50-100x slower with `MOZ_CHAOSMODE=0xfb`.
Bug 1734020 Comment 7 Edit History
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Reading the notes in comment 0 here... I wonder if the "Altering thread scheduling", "Delay dispatching threads", and "Delay task running" items there might cause **particular slowness for style-system tests**, since our style system is multi-threaded. That would explain why `outline-valid-mandatory.html`'s seemingly-benign calls to `test_valid_value()` (which resolves some CSS) would end up being 50-100x slower with `MOZ_CHAOSMODE=0xfb`.