STR: 1. Enable gfx.webrender.all and gfx.webrender.debug.slow-frame-indicator prefs. 2. Load a Google Doc such as: https://docs.google.com/document/d/1CTaWucldHxEri5BUB1kL4faF4prwPlBa31yHFd-l8uc/edit 3. Scroll the doc until any flashing cursors are out of the viewport. 4. Mouse over the doc's text. RESULT: On Windows, WebRender's slow frame indicator keeps moving even though nothing on the page appears to be dirty. I was NOT able to reproduce this Google Doc problem with WebRender on macOS.

Here is about:support for my Windows laptop: Application Basics ------------------ Name: Firefox Version: 65.0a1 Build ID: 20181127100134 Update Channel: nightly User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:65.0) Gecko/20100101 Firefox/65.0 OS: Windows_NT 10.0 Multiprocess Windows: 4/4 (Enabled by user) Web Content Processes: 9/7 Enterprise Policies: Inactive Google Key: Found Mozilla Location Service Key: Found Safe Mode: false 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: 000000000000e9a7) EGL_VERSION: 1.4 (ANGLE 2.1.0.790e8e6b4179) 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_MOZ_create_context_provoking_vertex_dont_care 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 WebGL 1 Driver Renderer: Google Inc. -- ANGLE (Intel(R) HD Graphics 530 Direct3D11 vs_5_0 ps_5_0) WebGL 1 Driver Version: OpenGL ES 2.0 (ANGLE 2.1.0.790e8e6b4179) 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_pack_reverse_row_order GL_ANGLE_program_cache_control 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_sync_query 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_frag_depth 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_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_compressed_ETC1_RGB8_texture 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_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_frag_depth EXT_sRGB EXT_shader_texture_lod EXT_texture_filter_anisotropic EXT_disjoint_timer_query 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: 000000000000e9a7) EGL_VERSION: 1.4 (ANGLE 2.1.0.790e8e6b4179) 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_MOZ_create_context_provoking_vertex_dont_care 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 WebGL 2 Driver Renderer: Google Inc. -- ANGLE (Intel(R) HD Graphics 530 Direct3D11 vs_5_0 ps_5_0) WebGL 2 Driver Version: OpenGL ES 3.0 (ANGLE 2.1.0.790e8e6b4179) WebGL 2 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_multiview GL_ANGLE_pack_reverse_row_order GL_ANGLE_program_cache_control 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_sync_query 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_frag_depth 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_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_compressed_ETC1_RGB8_texture 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_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 2 Extensions: EXT_color_buffer_float EXT_texture_filter_anisotropic EXT_disjoint_timer_query OES_texture_float_linear 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 DirectWrite: true (10.0.17763.1) GPU #1 Active: Yes Description: Intel(R) HD Graphics 530 Vendor ID: 0x8086 Device ID: 0x191b Driver Version: 25.20.100.6373 Driver Date: 10-31-2018 Drivers: igdumdim64 igd10iumd64 igd10iumd64 igd12umd64 igdumdim32 igd10iumd32 igd10iumd32 igd12umd32 Subsys ID: 674e1a58 RAM: Unknown GPU #2 Active: No Description: NVIDIA GeForce GTX 970M Vendor ID: 0x10de Device ID: 0x13d8 Driver Version: 23.21.13.8873 Driver Date: 12-18-2017 Drivers: C:\WINDOWS\System32\DriverStore\FileRepository\nvrz.inf_amd64_7550cbd75f58b6c2\nvldumdx.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvrz.inf_amd64_7550cbd75f58b6c2\nvldumdx.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvrz.inf_amd64_7550cbd75f58b6c2\nvldumdx.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvrz.inf_amd64_7550cbd75f58b6c2\nvldumdx.dll C:\WINDOWS\System32\DriverStore\FileRepository\nvrz.inf_amd64_7550cbd75f58b6c2\nvldumd.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvrz.inf_amd64_7550cbd75f58b6c2\nvldumd.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvrz.inf_amd64_7550cbd75f58b6c2\nvldumd.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvrz.inf_amd64_7550cbd75f58b6c2\nvldumd.dll Subsys ID: 674e1a58 RAM: 6144 Diagnostics ClearType Parameters: Gamma: 2.2 Pixel Structure: RGB ClearType Level: 100 Enhanced Contrast: 50 AzureCanvasAccelerated: 0 AzureCanvasBackend: direct2d 1.1 AzureCanvasBackend (UI Process): skia AzureContentBackend: skia AzureContentBackend (UI Process): skia AzureFallbackCanvasBackend (UI Process): cairo Slow Frame #01: Frame 219(https://docs.google.com/document/d/1vITDHIxST0T-1gB8CqIAI51UYur3xhsq0H1tetbHeHo/edit?ts=5bfc4a26#heading=h.kc9qkx8t4bgh) CONTENT_FRAME_TIME 9792 - Transaction start 0.082700, main-thread time 2.606300, full paint time 1491.485900, Skipped composites 0, Composite start 1625.406400, Resource upload time 0.034400, GPU cache upload time 1.104000, Render time 4.072100, Composite time 7.202700 Slow Frame #02: Frame 220(https://docs.google.com/document/d/1vITDHIxST0T-1gB8CqIAI51UYur3xhsq0H1tetbHeHo/edit?ts=5bfc4a26#heading=h.kc9qkx8t4bgh) CONTENT_FRAME_TIME 9127 - Transaction start 0.578800, main-thread time 9.888200, full paint time 1383.667500, Skipped composites 0, Composite start 1514.988600, Resource upload time 0.034400, GPU cache upload time 1.104000, Render time 4.072100, Composite time 7.202700 Slow Frame #03: Frame 1(about:blank) CONTENT_FRAME_TIME 6137 - Transaction start 0.000000, main-thread time 0.330700, full paint time 0.717300, Skipped composites 0, Composite start 978.187500, Resource upload time 2.557000, GPU cache upload time 0.066000, Render time 15.362300, Composite time 45.029500 Slow Frame #04: Frame 3(chrome://gfxsanity/content/sanitytest.html) CONTENT_FRAME_TIME 4455 - Transaction start 0.044700, main-thread time 0.270400, full paint time 0.831700, Skipped composites 0, Composite start 635.187800, Resource upload time 0.000400, GPU cache upload time 0.054700, Render time 107.317000, Composite time 107.610200 Slow Frame #05: Frame 2(https://docs.google.com/document/d/1MO-U0xTiAsO0CiG7E6HWBQu2JSNy7hu10J4RX6CJXHo/edit#heading=h.xxepy32y9d1q) CONTENT_FRAME_TIME 4378 - Transaction start 0.524600, main-thread time 6.339100, full paint time 28.144200, Skipped composites 0, Composite start 36.077800, Resource upload time 28.942900, GPU cache upload time 0.722900, Render time 690.607800, Composite time 694.403000 Slow Frame #06: Frame 1(about:blank) CONTENT_FRAME_TIME 4256 - Transaction start 0.000000, main-thread time 0.084600, full paint time 0.734800, Skipped composites 0, Composite start 679.927600, Resource upload time 6.363300, GPU cache upload time 0.091300, Render time 28.426300, Composite time 29.558500 Slow Frame #07: Frame 2(chrome://gfxsanity/content/sanitytest.html) CONTENT_FRAME_TIME 4014 - Transaction start 1.580900, main-thread time 0.424000, full paint time 0.843900, Skipped composites 0, Composite start 17.407200, Resource upload time 0.000700, GPU cache upload time 0.057100, Render time 1.147900, Composite time 653.293400 Slow Frame #08: Frame 86(https://twitter.com/womenstilltrash/status/1066095291252776961) CONTENT_FRAME_TIME 3881 - Transaction start 5.671800, main-thread time 10.834100, full paint time 20.359800, Skipped composites 0, Composite start 27.288900, Resource upload time 0.001000, GPU cache upload time 0.608200, Render time 616.583900, Composite time 625.381800 Slow Frame #09: Frame 40(https://docs.google.com/document/d/1MO-U0xTiAsO0CiG7E6HWBQu2JSNy7hu10J4RX6CJXHo/edit#heading=h.xxepy32y9d1q) CONTENT_FRAME_TIME 3773 - Transaction start 38.489200, main-thread time 5.038100, full paint time 6.955800, Skipped composites 0, Composite start 657.898500, Resource upload time 0.239700, GPU cache upload time 1.054000, Render time 4.447100, Composite time 9.590700 Slow Frame #10: Frame 1(about:blank) CONTENT_FRAME_TIME 3629 - Transaction start 0.000000, main-thread time 0.047100, full paint time 0.446400, Skipped composites 0, Composite start 495.050800, Resource upload time 0.057400, GPU cache upload time 0.073700, Render time 1.576100, Composite time 109.929700 GPUProcessPid: 14364 GPUProcess: Terminate GPU Process Device Reset: Trigger Device Reset ClearType Parameters: Gamma: 2.2 Pixel Structure: RGB ClearType Level: 100 Enhanced Contrast: 50 failures: GP+[GFX1-]: Updating unknown shared surface: 377957122168 Decision Log WEBRENDER: opt-in by default: WebRender is an opt-in feature available by user: Force enabled by pref WEBRENDER_QUALIFIED: blocked by env: Has battery Failure Log (#0): GP+[GFX1-]: Updating unknown shared surface: 377957122168 (#1): GP+[GFX1-]: Updating unknown shared surface: 382252089412

I'm unable to reproduce on Windows (though I'm not logged in). Can you grab a profile of it happening? Make sure you add "RenderBackend,Renderer,WebRender,Wr" to the threads list in profiler ui.

And my guess is this is some blob image thing gone bad.

After some more investigation, I see that this problem only happens scrolling the Google Doc (I'm using my laptop's track pad) when my laptop is running on *battery power*. Scrolling seems to reproduce the problem more easily than mousing over the doc. My laptop has an integrated Intel GPU and a discrete NVIDIA GPU. I used the NVIDIA Control Panel to force the NVIDIA GPU, but my about:support says my "Intel(R) HD Graphics 530" GPU #1 is active and my "NVIDIA GeForce GTX 970M" GPU #2 is inactive. When switching between AC and battery power and refreshing about:support always shows my Intel GPU as active, never the NVIDIA GPU. Profile of scrolling on AC power with no slow frame indicator activity: http://bit.ly/2Rhv4uD Profile of scrolling on battery power with continuous slow frame indicator activity: http://bit.ly/2RfFU4c