Steps to reproduce

1. Enable fission.autostart
2. Load https://haxe.org/blog/flowplay-casestudy/
3. Quickly scroll up and down the page by clicking and dragging the scrollbar thumb. I'm using a Windows laptop and trackpad, if that matters.

Expected results

Smooth scrolling with no flashing or checkerboarding.

Actual results

The page will start flashing when you scroll past the screenshots at the bottom of the page.

I can reproduce at least as far back as 69 Nightly (2019-06-06). The problem is intermittent, so I wasn't able to bisect a stable regression range but this problem might be a regression from OOP iframe bug 1451455:

https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=e3a716b620264d9e345c325d578d7c756939c293&tochange=49dfd67a3ba84d0c26fc59508c8ae0ee2c5bdbe7

@ Botond, Fission triage think this bug looks an APZ bug. This bug should block enabling Fission Nightly (Fission's M6 milestone for Q2).

Note that I only see this bug when clicking and dragging scroll bar thumb using my Windows laptop's trackpad. I don't see this bug when scrolling with two-finger trackpad gesture. When the page is flashing, the scroll bar thumb itself jumps rapidly between the top of the scroll bar and the actual scroll position as I drag it. The jumping only happens when the scroll bar thumb is on the bottom half of the scroll bar. Maybe there is some event coordinate mapping bug or overflow?

I'm running Windows 10.0.19041 (Windows Insider "Slow" channel Build 19041) on a Dell XPS 15 9570 laptop. If you need any more detail system info, just let me know.

Here is my about:support info:

Application Basics

Name: Firefox
Version: 74.0a1
Build ID: 20200113093823
Update Channel: nightly
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:74.0) Gecko/20100101 Firefox/74.0
OS: Windows_NT 10.0
Launcher Process: Enabled
Multiprocess Windows: 5/5 Enabled by default
Remote Processes: 10
Enterprise Policies: Inactive
Google Location Service Key: Found
Google Safebrowsing Key: Found
Mozilla Location Service Key: Found
Safe Mode: false

Nightly Features

Name: DoH Roll-Out
Version: 1.3.0
ID: doh-rollout@mozilla.org

Name: Firefox Screenshots
Version: 39.0.0
ID: screenshots@mozilla.org

Name: Form Autofill
Version: 1.0
ID: formautofill@mozilla.org

Name: Web Compat
Version: 6.4.0
ID: webcompat@mozilla.org

Name: WebCompat Reporter
Version: 1.1.0
ID: webcompat-reporter@mozilla.org

Remote Processes

Type: Web Content
Count: 2 / 8

Type: Isolated Web Content
Count: 6

Type: Extension
Count: 1

Type: GPU
Count: 1

Graphics

Features
Compositing: WebRender
Asynchronous Pan/Zoom: wheel input enabled; touch input enabled; scrollbar drag enabled; keyboard enabled; autoscroll enabled
WebGL 1 Driver WSI Info: EGL_VENDOR: Google Inc. (adapter LUID: 0000000000011053) EGL_VERSION: 1.4 (ANGLE 2.1.0.5eaf76b0bfd1) EGL_EXTENSIONS: EGL_EXT_create_context_robustness EGL_ANGLE_d3d_share_handle_client_buffer EGL_ANGLE_d3d_texture_client_buffer EGL_ANGLE_surface_d3d_texture_2d_share_handle EGL_ANGLE_query_surface_pointer EGL_ANGLE_window_fixed_size EGL_ANGLE_keyed_mutex EGL_ANGLE_surface_orientation EGL_ANGLE_direct_composition EGL_NV_post_sub_buffer EGL_KHR_create_context EGL_EXT_device_query EGL_KHR_image EGL_KHR_image_base EGL_KHR_gl_texture_2D_image EGL_KHR_gl_texture_cubemap_image EGL_KHR_gl_renderbuffer_image EGL_KHR_get_all_proc_addresses EGL_KHR_stream EGL_KHR_stream_consumer_gltexture EGL_NV_stream_consumer_gltexture_yuv EGL_ANGLE_flexible_surface_compatibility EGL_ANGLE_stream_producer_d3d_texture EGL_ANGLE_create_context_webgl_compatibility EGL_CHROMIUM_create_context_bind_generates_resource EGL_CHROMIUM_sync_control EGL_EXT_pixel_format_float EGL_KHR_surfaceless_context EGL_ANGLE_display_texture_share_group EGL_ANGLE_create_context_client_arrays EGL_ANGLE_program_cache_control EGL_ANGLE_robust_resource_initialization EGL_ANGLE_create_context_extensions_enabled EGL_ANDROID_blob_cache EGL_ANDROID_recordable EGL_ANGLE_image_d3d11_texture EGL_ANGLE_create_context_backwards_compatible EGL_EXTENSIONS(nullptr): EGL_EXT_client_extensions EGL_EXT_platform_base EGL_EXT_platform_device EGL_ANGLE_platform_angle EGL_ANGLE_platform_angle_d3d EGL_ANGLE_device_creation EGL_ANGLE_device_creation_d3d11 EGL_ANGLE_experimental_present_path EGL_KHR_client_get_all_proc_addresses EGL_KHR_debug EGL_ANGLE_explicit_context EGL_ANGLE_feature_control
WebGL 1 Driver Renderer: Google Inc. -- ANGLE (Intel(R) UHD Graphics 630 Direct3D11 vs_5_0 ps_5_0)
WebGL 1 Driver Version: OpenGL ES 2.0.0 (ANGLE 2.1.0.5eaf76b0bfd1)
WebGL 1 Driver Extensions: GL_ANGLE_client_arrays GL_ANGLE_depth_texture GL_ANGLE_explicit_context GL_ANGLE_explicit_context_gles1 GL_ANGLE_framebuffer_blit GL_ANGLE_framebuffer_multisample GL_ANGLE_instanced_arrays GL_ANGLE_lossy_etc_decode GL_ANGLE_memory_size GL_ANGLE_multi_draw GL_ANGLE_multiview_multisample GL_ANGLE_pack_reverse_row_order GL_ANGLE_program_cache_control GL_ANGLE_provoking_vertex GL_ANGLE_request_extension GL_ANGLE_robust_client_memory GL_ANGLE_texture_compression_dxt3 GL_ANGLE_texture_compression_dxt5 GL_ANGLE_texture_usage GL_ANGLE_translated_shader_source GL_CHROMIUM_bind_generates_resource GL_CHROMIUM_bind_uniform_location GL_CHROMIUM_color_buffer_float_rgb GL_CHROMIUM_color_buffer_float_rgba GL_CHROMIUM_copy_compressed_texture GL_CHROMIUM_copy_texture GL_CHROMIUM_lose_context GL_CHROMIUM_sync_query GL_EXT_blend_func_extended GL_EXT_blend_minmax GL_EXT_color_buffer_half_float GL_EXT_debug_marker GL_EXT_discard_framebuffer GL_EXT_disjoint_timer_query GL_EXT_draw_buffers GL_EXT_float_blend GL_EXT_frag_depth GL_EXT_instanced_arrays GL_EXT_map_buffer_range GL_EXT_occlusion_query_boolean GL_EXT_read_format_bgra GL_EXT_robustness GL_EXT_sRGB GL_EXT_shader_texture_lod GL_EXT_texture_compression_bptc GL_EXT_texture_compression_dxt1 GL_EXT_texture_compression_s3tc_srgb GL_EXT_texture_filter_anisotropic GL_EXT_texture_format_BGRA8888 GL_EXT_texture_rg GL_EXT_texture_storage GL_EXT_unpack_subimage GL_KHR_debug GL_KHR_parallel_shader_compile GL_KHR_robust_buffer_access_behavior GL_NV_EGL_stream_consumer_external GL_NV_fence GL_NV_pack_subimage GL_NV_pixel_buffer_object GL_OES_EGL_image GL_OES_EGL_image_external GL_OES_depth24 GL_OES_depth32 GL_OES_element_index_uint GL_OES_get_program_binary GL_OES_mapbuffer GL_OES_packed_depth_stencil GL_OES_rgb8_rgba8 GL_OES_standard_derivatives GL_OES_surfaceless_context GL_OES_texture_3D GL_OES_texture_border_clamp GL_OES_texture_float GL_OES_texture_float_linear GL_OES_texture_half_float GL_OES_texture_half_float_linear GL_OES_texture_npot GL_OES_vertex_array_object OES_compressed_EAC_R11_signed_texture OES_compressed_EAC_R11_unsigned_texture OES_compressed_EAC_RG11_signed_texture OES_compressed_EAC_RG11_unsigned_texture OES_compressed_ETC2_RGB8_texture OES_compressed_ETC2_RGBA8_texture OES_compressed_ETC2_punchthroughA_RGBA8_texture OES_compressed_ETC2_punchthroughA_sRGB8_alpha_texture OES_compressed_ETC2_sRGB8_alpha8_texture OES_compressed_ETC2_sRGB8_texture
WebGL 1 Extensions: ANGLE_instanced_arrays EXT_blend_minmax EXT_color_buffer_half_float EXT_float_blend EXT_frag_depth EXT_shader_texture_lod EXT_sRGB EXT_texture_compression_bptc EXT_texture_filter_anisotropic MOZ_debug OES_element_index_uint OES_standard_derivatives OES_texture_float OES_texture_float_linear OES_texture_half_float OES_texture_half_float_linear OES_vertex_array_object WEBGL_color_buffer_float WEBGL_compressed_texture_s3tc WEBGL_compressed_texture_s3tc_srgb WEBGL_debug_renderer_info WEBGL_debug_shaders WEBGL_depth_texture WEBGL_draw_buffers WEBGL_lose_context
WebGL 2 Driver WSI Info: EGL_VENDOR: Google Inc. (adapter LUID: 0000000000011053) EGL_VERSION: 1.4 (ANGLE 2.1.0.5eaf76b0bfd1) EGL_EXTENSIONS: EGL_EXT_create_context_robustness EGL_ANGLE_d3d_share_handle_client_buffer EGL_ANGLE_d3d_texture_client_buffer EGL_ANGLE_surface_d3d_texture_2d_share_handle EGL_ANGLE_query_surface_pointer EGL_ANGLE_window_fixed_size EGL_ANGLE_keyed_mutex EGL_ANGLE_surface_orientation EGL_ANGLE_direct_composition EGL_NV_post_sub_buffer EGL_KHR_create_context EGL_EXT_device_query EGL_KHR_image EGL_KHR_image_base EGL_KHR_gl_texture_2D_image EGL_KHR_gl_texture_cubemap_image EGL_KHR_gl_renderbuffer_image EGL_KHR_get_all_proc_addresses EGL_KHR_stream EGL_KHR_stream_consumer_gltexture EGL_NV_stream_consumer_gltexture_yuv EGL_ANGLE_flexible_surface_compatibility EGL_ANGLE_stream_producer_d3d_texture EGL_ANGLE_create_context_webgl_compatibility EGL_CHROMIUM_create_context_bind_generates_resource EGL_CHROMIUM_sync_control EGL_EXT_pixel_format_float EGL_KHR_surfaceless_context EGL_ANGLE_display_texture_share_group EGL_ANGLE_create_context_client_arrays EGL_ANGLE_program_cache_control EGL_ANGLE_robust_resource_initialization EGL_ANGLE_create_context_extensions_enabled EGL_ANDROID_blob_cache EGL_ANDROID_recordable EGL_ANGLE_image_d3d11_texture EGL_ANGLE_create_context_backwards_compatible EGL_EXTENSIONS(nullptr): EGL_EXT_client_extensions EGL_EXT_platform_base EGL_EXT_platform_device EGL_ANGLE_platform_angle EGL_ANGLE_platform_angle_d3d EGL_ANGLE_device_creation EGL_ANGLE_device_creation_d3d11 EGL_ANGLE_experimental_present_path EGL_KHR_client_get_all_proc_addresses EGL_KHR_debug EGL_ANGLE_explicit_context EGL_ANGLE_feature_control
WebGL 2 Driver Renderer: Google Inc. -- ANGLE (Intel(R) UHD Graphics 630 Direct3D11 vs_5_0 ps_5_0)
WebGL 2 Driver Version: OpenGL ES 3.0.0 (ANGLE 2.1.0.5eaf76b0bfd1)
WebGL 2 Driver Extensions: GL_ANGLE_client_arrays GL_ANGLE_copy_texture_3d GL_ANGLE_depth_texture GL_ANGLE_explicit_context GL_ANGLE_explicit_context_gles1 GL_ANGLE_framebuffer_blit GL_ANGLE_framebuffer_multisample GL_ANGLE_instanced_arrays GL_ANGLE_lossy_etc_decode GL_ANGLE_memory_size GL_ANGLE_multi_draw GL_ANGLE_multiview_multisample GL_ANGLE_pack_reverse_row_order GL_ANGLE_program_cache_control GL_ANGLE_provoking_vertex GL_ANGLE_request_extension GL_ANGLE_robust_client_memory GL_ANGLE_texture_compression_dxt3 GL_ANGLE_texture_compression_dxt5 GL_ANGLE_texture_multisample GL_ANGLE_texture_usage GL_ANGLE_translated_shader_source GL_CHROMIUM_bind_generates_resource GL_CHROMIUM_bind_uniform_location GL_CHROMIUM_color_buffer_float_rgb GL_CHROMIUM_color_buffer_float_rgba GL_CHROMIUM_copy_compressed_texture GL_CHROMIUM_copy_texture GL_CHROMIUM_lose_context GL_CHROMIUM_sync_query GL_EXT_blend_func_extended GL_EXT_blend_minmax GL_EXT_color_buffer_float GL_EXT_color_buffer_half_float GL_EXT_debug_marker GL_EXT_discard_framebuffer GL_EXT_disjoint_timer_query GL_EXT_draw_buffers GL_EXT_float_blend GL_EXT_frag_depth GL_EXT_instanced_arrays GL_EXT_map_buffer_range GL_EXT_occlusion_query_boolean GL_EXT_read_format_bgra GL_EXT_robustness GL_EXT_sRGB GL_EXT_shader_texture_lod GL_EXT_texture_compression_bptc GL_EXT_texture_compression_dxt1 GL_EXT_texture_compression_s3tc_srgb GL_EXT_texture_filter_anisotropic GL_EXT_texture_format_BGRA8888 GL_EXT_texture_norm16 GL_EXT_texture_rg GL_EXT_texture_storage GL_EXT_unpack_subimage GL_KHR_debug GL_KHR_parallel_shader_compile GL_KHR_robust_buffer_access_behavior GL_NV_EGL_stream_consumer_external GL_NV_fence GL_NV_pack_subimage GL_NV_pixel_buffer_object GL_OES_EGL_image GL_OES_EGL_image_external GL_OES_EGL_image_external_essl3 GL_OES_depth24 GL_OES_depth32 GL_OES_element_index_uint GL_OES_get_program_binary GL_OES_mapbuffer GL_OES_packed_depth_stencil GL_OES_rgb8_rgba8 GL_OES_standard_derivatives GL_OES_surfaceless_context GL_OES_texture_3D GL_OES_texture_border_clamp GL_OES_texture_float GL_OES_texture_float_linear GL_OES_texture_half_float GL_OES_texture_half_float_linear GL_OES_texture_npot GL_OES_vertex_array_object GL_OVR_multiview GL_OVR_multiview2 OES_compressed_EAC_R11_signed_texture OES_compressed_EAC_R11_unsigned_texture OES_compressed_EAC_RG11_signed_texture OES_compressed_EAC_RG11_unsigned_texture OES_compressed_ETC2_RGB8_texture OES_compressed_ETC2_RGBA8_texture OES_compressed_ETC2_punchthroughA_RGBA8_texture OES_compressed_ETC2_punchthroughA_sRGB8_alpha_texture OES_compressed_ETC2_sRGB8_alpha8_texture OES_compressed_ETC2_sRGB8_texture
WebGL 2 Extensions: EXT_color_buffer_float EXT_float_blend EXT_texture_compression_bptc EXT_texture_filter_anisotropic MOZ_debug OES_texture_float_linear OVR_multiview2 WEBGL_compressed_texture_s3tc WEBGL_compressed_texture_s3tc_srgb WEBGL_debug_renderer_info WEBGL_debug_shaders WEBGL_lose_context
Direct2D: true
Uses Tiling (Content): true
Off Main Thread Painting Enabled: true
Off Main Thread Painting Worker Count: 4
Target Frame Rate: 60
DirectWrite: true (10.0.19041.1)
GPU #1
Active: Yes
Description: Intel(R) UHD Graphics 630
Vendor ID: 0x8086
Device ID: 0x3e9b
Driver Version: 26.20.100.7262
Driver Date: 9-25-2019
Drivers: igdumdim64 igd10iumd64 igd10iumd64 igd12umd64 igdumdim32 igd10iumd32 igd10iumd32 igd12umd32
Subsys ID: 087c1028
RAM: 0
GPU #2
Active: No
Description: NVIDIA GeForce GTX 1050 Ti with Max-Q Design
Vendor ID: 0x10de
Device ID: 0x1c8c
Driver Version: 26.21.14.4145
Driver Date: 11-26-2019
Drivers: C:\WINDOWS\System32\DriverStore\FileRepository\nvdm.inf_amd64_e7b78a9895fd9527\nvldumdx.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvdm.inf_amd64_e7b78a9895fd9527\nvldumdx.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvdm.inf_amd64_e7b78a9895fd9527\nvldumdx.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvdm.inf_amd64_e7b78a9895fd9527\nvldumdx.dll C:\WINDOWS\System32\DriverStore\FileRepository\nvdm.inf_amd64_e7b78a9895fd9527\nvldumd.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvdm.inf_amd64_e7b78a9895fd9527\nvldumd.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvdm.inf_amd64_e7b78a9895fd9527\nvldumd.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvdm.inf_amd64_e7b78a9895fd9527\nvldumd.dll
Subsys ID: 087c1028
RAM: 4096
Diagnostics
AzureCanvasBackend: direct2d 1.1
AzureCanvasBackend (UI Process): skia
AzureContentBackend: skia
AzureContentBackend (UI Process): skia
AzureFallbackCanvasBackend (UI Process): none
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Display0: 3840x2160@60Hz
DisplayCount: 1
GPUProcessPid: 1300
GPUProcess: Terminate GPU Process
Device Reset: Trigger Device Reset
ClearType Parameters: Gamma: 1.8 Pixel Structure: RGB ClearType Level: 100 Enhanced Contrast: 50
Decision Log
WEBRENDER:
opt-in by default: WebRender is an opt-in feature
available by user: Force enabled by pref
WEBRENDER_QUALIFIED:
blocked-has-battery by env: Has battery
WEBRENDER_COMPOSITOR:
disabled by default: Disabled by default
WEBGPU:
disabled by default: Disabled by default

Failure Log
(#0): CP+[GFX1-]: Failed to connect WebRenderBridgeChild.
(#1): CP+[GFX1-]: Failed to connect WebRenderBridgeChild.

Media

Audio Backend: wasapi
Max Channels: 2
Preferred Sample Rate: 48000
Output Devices
Name: Group
Headset (Chris's Bose QC35 II Hands-Free AG Audio): BTHHFENUM\BthHFPAudio\8&21080539&0&97
T24C550 (Intel(R) Display Audio):
Speakers/Headphones (Realtek(R) Audio): INTELAUDIO\FUNC_01&VEN_10EC&DEV_0298&SUBSYS_1028087C&REV_1001\4&2223f159&0&0001
PJD7820HD (Intel(R) Display Audio):
:
E430i-C2 (Intel(R) Display Audio): INTELAUDIO\FUNC_01&VEN_8086&DEV_280B&SUBSYS_80860101&REV_1000\4&2223f159&0&0201
DELL ST2210 (Intel(R) Display Audio): INTELAUDIO\FUNC_01&VEN_8086&DEV_280B&SUBSYS_80860101&REV_1000\4&2223f159&0&0201
:
Headphones (2- Chris's Bose QC35 II Stereo): BTHENUM{0000110b-0000-1000-8000-00805f9b34fb}_VID&0001009e_PID&4020\7&202dcc8d&0&2C41A149213C_C00000000
LG TV (Intel(R) Display Audio): INTELAUDIO\FUNC_01&VEN_8086&DEV_280B&SUBSYS_80860101&REV_1000\4&2223f159&0&0201
DELL ST2210 (Intel(R) Display Audio): INTELAUDIO\FUNC_01&VEN_8086&DEV_280B&SUBSYS_80860101&REV_1000\4&2223f159&0&0201
T24C550 (Intel(R) Display Audio): INTELAUDIO\FUNC_01&VEN_8086&DEV_280B&SUBSYS_80860101&REV_1000\4&2223f159&0&0201
:
DELL E2318H (Intel(R) Display Audio):
Input Devices
Name: Group
:
Stereo Mix (Realtek(R) Audio): INTELAUDIO\FUNC_01&VEN_10EC&DEV_0298&SUBSYS_1028087C&REV_1001\4&2223f159&0&0001
Microphone (Realtek(R) Audio): INTELAUDIO\FUNC_01&VEN_10EC&DEV_0298&SUBSYS_1028087C&REV_1001\4&2223f159&0&0001
:
:
Headset (Chris's Bose QC35 II Hands-Free AG Audio): BTHHFENUM\BthHFPAudio\8&21080539&0&97
Media Capabilities
Enumerate database

I haven't been able to reproduce this. I tested today's nightly in a clean profile (with mozregression --pref fission.autostart:true --launch 2020-01-20), on Windows, dragging the scrollbar with the trackpad. (Previously to that I tried Linux, again with scrollbar dragging.)

(In reply to Chris Peterson [:cpeterson] from comment #1)

When the page is flashing, the scroll bar thumb itself jumps rapidly between the top of the scroll bar and the actual scroll position as I drag it.

This symptom makes me wonder if the issue is related to the slider.snapMultiplier feature.

Chris, can you reproduce the issue if you set slider.snapMultiplier=0? Note, the pref requires a restart.

(In reply to Botond Ballo [:botond] from comment #2)

I haven't been able to reproduce this. I tested today's nightly in a clean profile (with mozregression --pref fission.autostart:true --launch 2020-01-20), on Windows, dragging the scrollbar with the trackpad. (Previously to that I tried Linux, again with scrollbar dragging.)

I can still reproduce this bug, but it is much harder to reproduce. It used to happen nearly all the time, but now it only happens maybe 1/20 times. This makes me suspect something outside Firefox changed, such as a Windows Update.

When the bug does reproduce, it seems like it might happen if I move the mouse pointer over the page or outside the window so that the scroll thumb jumps back to its original position and/or click and release the scroll thumb a couple times.

Chris, can you reproduce the issue if you set slider.snapMultiplier=0? Note, the pref requires a restart.

Since I can no longer reliably reproduce the bug, I can't test whether slider.snapMultiplier=0 makes the problem go away.

Perhaps we can dump this bug in the P5 bug backlog until I or someone else has better STR?

Sounds good! I'm happy to investigate if I can reproduce.

I can no longer reproduce this Fission bug. I think we can close it.