Is this happening on any high speed downloads, or only on specific types (like video). Could you please capture a performance profile during one of these high speed downloads? That may help with assigning the bug to the most appropriate component See https://profiler.firefox.com/ for instructions.
Bug 1972941 Comment 2 Edit History
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Is this happening on any high speed downloads, or only on specific types (like video). Any sharable URL where you can easily reproduce this? Could you please capture a performance profile during one of these high speed downloads? That may help with assigning the bug to the most appropriate component See https://profiler.firefox.com/ for instructions.