Probably Bug 1588484 really just made this easier to see/trigger (by making rendering a bit more async, or something along those lines), rather than being directly responsible. I captured a profile of myself scrolling slowly down the page until the bug starts reproducing. (Notably, it only starts happening once you've scrolled far enough): https://share.firefox.dev/46WCsTJ The first flicker happens at about t=24.98s, here: https://share.firefox.dev/3XaN1PZ I think this might be from some frame reconstruction, if I'm reading the profile correctly. Here's another profile where I reduced the page substantially (by adding `display:none` to a bunch of unnecessary content/ads, while preserving the bug), and then scrolled up and down, to get more samples of just-the-actions-that-trigger-the-bug. I think I've isolated the issue; more details in next comment.
Bug 1910887 Comment 5 Edit History
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Probably Bug 1588484 really just made this easier to see/trigger (by making rendering a bit more async, or something along those lines), rather than being directly responsible. I captured a profile of myself scrolling slowly down the page until the bug starts reproducing. (Notably, it only starts happening once you've scrolled far enough): https://share.firefox.dev/46WCsTJ The first flicker happens at about t=24.98s, here: https://share.firefox.dev/3XaN1PZ I think this might be from some frame reconstruction, if I'm reading the profile correctly. Here's another profile where I reduced the page substantially (by adding `display:none` to a bunch of unnecessary content/ads, while preserving the bug), and then scrolled up and down, to get more samples of just-the-actions-that-trigger-the-bug: https://share.firefox.dev/3X6VnIa I think I've isolated the issue; more details in next comment.