Cleopatra is almost unusably slow if you increase the Gecko Profiler buffer size (I use 90MB for example). I was wondering why that is today. It seems like our display list construction is extremely inefficient on this page. For example, see this profile: https://perfht.ml/2lSZEeH. We are spending 4.8 *seconds* in nsIFrame::BuildDisplayListForStackingContext(), in eight chunks of roughly the same size. This is easily visible if you for example try selecting a range in the timeline. Each click has a lag of seconds to have any effect. The profile in question from which the measurement was obtained is <https://perf-html.io/public/55385c23113278e8db31a2fee58338fdbf04bfd1/calltree/?search=topicListener&thread=1>.
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