**Affected Versions:** 84.0 - Beta RC 83.0 - Release - works with Rosetta installed **Unaffected Version:** Nightly (2020-12-08) **Affected Platforms:** ARM64 MacOS: - miniMac: MacOS Big Sur 11.0.1, Mac mini (M1, 2020), Chip: Apple M1, display 27-inch (2560x1440), with Rosetta **Unaffected Tested Platforms:** MacOS 10.15 MacBook Pro 13inch, macOS Big Sur 11 (intel chip) **Steps to reproduce:** 1. Go to https://ro.pinterest.com/pin/584342120393644748/ (log in when prompted) 2. While the video is played back start scrolling up and down 3. Reload the page once if needed (performance issues are not visible enough) 4. Start scrolling again and also check the hover highlight from the address bar search options for significant delays or open new tabs **Expected Results:** Scrolling on Pinterest while videos are played back should be smooth **Actual Result:** Severe performance issues can be observed if a video is played back while scrolling on Pinterest and the suggested images are being loaded. See recording: https://streamable.com/eymtu5 Severity suggestion: S1 - S2 - Pinterest is a common top site Not reproducible with Chrome using the same M1 device. Chrome nearly hits 25% CPU usage while Firefox can reach over 100% (please note macOS CPU usage shown in activity monitor is per core). Attached screenshots of core usage in Beta and Nightly (unaffected) The significant difference in Nightly (where this is not reproducible) is that it uses WebRender while on Beta and Release we have OpenGL. Performance Profile: https://profiler.firefox.com/from-addon/calltree/?globalTrackOrder=7-0-1-2-3-4-5-6&hiddenGlobalTracks=1-2-3-4-5&hiddenLocalTracksByPid=1148-1-2-3~1780-0-1-2-3-4-5&localTrackOrderByPid=1148-4-0-1-2-3~1780-6-0-1-2-3-4-5~&thread=10&v=5
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**Affected Versions:** 84.0 - Beta RC 83.0 - Release - works with Rosetta installed **Unaffected Version:** Nightly (2020-12-08) **Affected Platforms:** ARM64 MacOS: - miniMac: MacOS Big Sur 11.0.1, Mac mini (M1, 2020), Chip: Apple M1, display 27-inch (2560x1440), with Rosetta **Unaffected Tested Platforms:** MacOS 10.15 MacBook Pro 13inch, macOS Big Sur 11 (intel chip) **Steps to reproduce:** 1. Go to https://ro.pinterest.com/pin/584342120393644748/ (log in when prompted) 2. While the video is played back start scrolling up and down 3. Reload the page once if needed (performance issues are not visible enough) 4. Start scrolling again and also check the hover highlight from the address bar search options for significant delays or open new tabs **Expected Results:** Scrolling on Pinterest while videos are played back should be smooth **Actual Result:** Severe performance issues can be observed if a video is played back while scrolling on Pinterest and the suggested images are being loaded. See recording: https://streamable.com/eymtu5 **Severity suggestion: S1 - S2 - Pinterest is a common top site** Not reproducible with Chrome using the same M1 device. Chrome nearly hits 25% CPU usage while Firefox can reach over 100% (please note macOS CPU usage shown in activity monitor is per core). Attached screenshots of core usage in Beta and Nightly (unaffected) The significant difference in Nightly (where this is not reproducible) is that it uses WebRender while on Beta and Release we have OpenGL. Performance Profile: https://profiler.firefox.com/from-addon/calltree/?globalTrackOrder=7-0-1-2-3-4-5-6&hiddenGlobalTracks=1-2-3-4-5&hiddenLocalTracksByPid=1148-1-2-3~1780-0-1-2-3-4-5&localTrackOrderByPid=1148-4-0-1-2-3~1780-6-0-1-2-3-4-5~&thread=10&v=5
**Affected Versions:** 84.0 - Beta RC 83.0 - Release - works with Rosetta installed **Unaffected Version:** Nightly (2020-12-08) **Affected Platforms:** ARM64 MacOS: - miniMac: MacOS Big Sur 11.0.1, Mac mini (M1, 2020), Chip: Apple M1, display 27-inch (2560x1440), with Rosetta **Unaffected Tested Platforms:** MacOS 10.15 MacBook Pro 13inch, macOS Big Sur 11 (intel chip) **Steps to reproduce:** 1. Go to https://ro.pinterest.com/pin/584342120393644748/ (log in when prompted)(make sure the browser is maximized) 2. While the video is played back start scrolling up and down 3. Reload the page once if needed (performance issues are not visible enough) 4. Start scrolling again and also check the hover highlight from the address bar search options for significant delays or open new tabs **Expected Results:** Scrolling on Pinterest while videos are played back should be smooth **Actual Result:** Severe performance issues can be observed if a video is played back while scrolling on Pinterest and the suggested images are being loaded. See recording: https://streamable.com/eymtu5 **Severity suggestion: S1 - S2 - Pinterest is a common top site** Not reproducible with Chrome using the same M1 device. Chrome nearly hits 25% CPU usage while Firefox can reach over 100% (please note macOS CPU usage shown in activity monitor is per core). Attached screenshots of core usage in Beta and Nightly (unaffected) The significant difference in Nightly (where this is not reproducible) is that it uses WebRender while on Beta and Release we have OpenGL. Performance Profile: https://profiler.firefox.com/from-addon/calltree/?globalTrackOrder=7-0-1-2-3-4-5-6&hiddenGlobalTracks=1-2-3-4-5&hiddenLocalTracksByPid=1148-1-2-3~1780-0-1-2-3-4-5&localTrackOrderByPid=1148-4-0-1-2-3~1780-6-0-1-2-3-4-5~&thread=10&v=5