Since upgrading to 66, the tab spinner (see screenshot) is happening a lot more than it used to, both on my Mac and my very beefy Windows 10 device at home.

Application Basics

Name: Firefox
Version: 66.0b5
Build ID: 20190204181317
Update Channel: beta
User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:66.0) Gecko/20100101 Firefox/66.0
OS: Darwin 18.0.0
Multiprocess Windows: 13/13 Enabled by default
Web Content Processes: 9/8
Enterprise Policies: Inactive
Google Key: Found
Mozilla Location Service Key: Found
Safe Mode: false

Crash Reports

All Crash Reports Firefox Features

Name: Firefox Screenshots
Version: 35.0.0
ID: screenshots@mozilla.org

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

Name: Web Compat
Version: 3.0.0
ID: webcompat@mozilla.org

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

Extensions

Name: APT GitHub Improvements
Version: 0.5.1
Enabled: true
ID: {32c53eee-8e02-464c-9ed6-bfdcee491acd}

Name: Facebook Container
Version: 1.4.2
Enabled: true
ID: @contain-facebook

Name: Firefox Multi-Account Containers
Version: 6.1.0
Enabled: true
ID: @testpilot-containers

Name: Min Vid
Version: 0.4.9
Enabled: true
ID: @min-vid

Name: Test Pilot
Version: 3.0.6vffecb95
Enabled: true
ID: @testpilot-addon

Name: Tile Tabs WE
Version: 11.8
Enabled: true
ID: tiletabs-we@DW-dev

Name: ZenHub for GitHub
Version: 2.38.37
Enabled: true
ID: zenhub@zenhub.io

Name: Adobe Acrobat
Version: 18.0.9
Enabled: false
ID: web2pdfextension.17@acrobat.adobe.com

Name: Stylus
Version: 1.5.2
Enabled: false
ID: {7a7a4a92-a2a0-41d1-9fd7-1e92480d612d}

Security Software
----------------- Type:

Type:

Type:

Graphics

Features
Compositing: OpenGL
asyncPanZoom: wheel input enabled; scrollbar drag enabled; keyboard enabled; autoscroll enabled
webgl1WSIInfo: CGL
WebGL 1 Driver Renderer: ATI Technologies Inc. -- AMD Radeon Pro 460 OpenGL Engine
WebGL 1 Driver Version: 4.1 ATI-2.0.36
WebGL 1 Driver Extensions: GL_ARB_blend_func_extended GL_ARB_draw_buffers_blend GL_ARB_draw_indirect GL_ARB_ES2_compatibility GL_ARB_explicit_attrib_location GL_ARB_gpu_shader_fp64 GL_ARB_gpu_shader5 GL_ARB_instanced_arrays GL_ARB_internalformat_query GL_ARB_occlusion_query2 GL_ARB_sample_shading GL_ARB_sampler_objects GL_ARB_separate_shader_objects GL_ARB_shader_bit_encoding GL_ARB_shader_subroutine GL_ARB_shading_language_include GL_ARB_tessellation_shader GL_ARB_texture_buffer_object_rgb32 GL_ARB_texture_cube_map_array GL_ARB_texture_gather GL_ARB_texture_query_lod GL_ARB_texture_rgb10_a2ui GL_ARB_texture_storage GL_ARB_texture_swizzle GL_ARB_timer_query GL_ARB_transform_feedback2 GL_ARB_transform_feedback3 GL_ARB_vertex_attrib_64bit GL_ARB_vertex_type_2_10_10_10_rev GL_ARB_viewport_array GL_EXT_debug_label GL_EXT_debug_marker GL_EXT_depth_bounds_test GL_EXT_texture_compression_s3tc GL_EXT_texture_filter_anisotropic GL_EXT_texture_mirror_clamp GL_EXT_texture_sRGB_decode GL_APPLE_client_storage GL_APPLE_container_object_shareable GL_APPLE_flush_render GL_APPLE_object_purgeable GL_APPLE_rgb_422 GL_APPLE_row_bytes GL_APPLE_texture_range GL_ATI_texture_mirror_once GL_NV_texture_barrier
WebGL 1 Extensions: ANGLE_instanced_arrays EXT_blend_minmax EXT_color_buffer_half_float EXT_texture_compression_rgtc 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: CGL
WebGL 2 Driver Renderer: ATI Technologies Inc. -- AMD Radeon Pro 460 OpenGL Engine
WebGL 2 Driver Version: 4.1 ATI-2.0.36
WebGL 2 Driver Extensions: GL_ARB_blend_func_extended GL_ARB_draw_buffers_blend GL_ARB_draw_indirect GL_ARB_ES2_compatibility GL_ARB_explicit_attrib_location GL_ARB_gpu_shader_fp64 GL_ARB_gpu_shader5 GL_ARB_instanced_arrays GL_ARB_internalformat_query GL_ARB_occlusion_query2 GL_ARB_sample_shading GL_ARB_sampler_objects GL_ARB_separate_shader_objects GL_ARB_shader_bit_encoding GL_ARB_shader_subroutine GL_ARB_shading_language_include GL_ARB_tessellation_shader GL_ARB_texture_buffer_object_rgb32 GL_ARB_texture_cube_map_array GL_ARB_texture_gather GL_ARB_texture_query_lod GL_ARB_texture_rgb10_a2ui GL_ARB_texture_storage GL_ARB_texture_swizzle GL_ARB_timer_query GL_ARB_transform_feedback2 GL_ARB_transform_feedback3 GL_ARB_vertex_attrib_64bit GL_ARB_vertex_type_2_10_10_10_rev GL_ARB_viewport_array GL_EXT_debug_label GL_EXT_debug_marker GL_EXT_depth_bounds_test GL_EXT_texture_compression_s3tc GL_EXT_texture_filter_anisotropic GL_EXT_texture_mirror_clamp GL_EXT_texture_sRGB_decode GL_APPLE_client_storage GL_APPLE_container_object_shareable GL_APPLE_flush_render GL_APPLE_object_purgeable GL_APPLE_rgb_422 GL_APPLE_row_bytes GL_APPLE_texture_range GL_ATI_texture_mirror_once GL_NV_texture_barrier
WebGL 2 Extensions: EXT_color_buffer_float EXT_texture_compression_rgtc 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
Uses Tiling: true
Uses Tiling (Content): true
Off Main Thread Painting Enabled: true
Off Main Thread Painting Worker Count: 4
Target Frame Rate: 60
GPU #1
Active: Yes
Vendor ID: 0x1002
Device ID: 0x67ef

Diagnostics
AzureCanvasAccelerated: 0
AzureCanvasBackend: skia
AzureContentBackend: skia
AzureFallbackCanvasBackend: none
TileHeight: 1024
TileWidth: 1024
Decision Log
WEBRENDER:
opt-in by default: WebRender is an opt-in feature
WEBRENDER_QUALIFIED:
blocked by env: No qualified hardware

Media

Audio Backend: audiounit
Max Channels: 2
Preferred Sample Rate: 44100
Output Devices
Name: Group
Headphones: AppleHDAEngineOutput:1F,3,0,1,1:0
DELL U2713H: AppleGFXHDAEngineOutputDP:0:{AC10-A092-30334D4C}
Input Devices
Name: Group
External Microphone: AppleHDAEngineInput:1F,3,0,1,0:1

Important Modified Preferences

accessibility.typeaheadfind.flashBar: 0
browser.cache.disk.capacity: 1048576
browser.cache.disk.filesystem_reported: 1
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browser.cache.disk.smart_size.first_run: false
browser.cache.disk.smart_size.use_old_max: false
browser.cache.frecency_experiment: 3
browser.places.smartBookmarksVersion: 8
browser.sessionstore.upgradeBackup.latestBuildID: 20190204181317
browser.startup.homepage_override.buildID: 20190204181317
browser.startup.homepage_override.mstone: 66.0
browser.tabs.remote.autostart.2: true
browser.tabs.warnOnClose: false
browser.urlbar.daysBeforeHidingSuggestionsPrompt: 0
browser.urlbar.lastSuggestionsPromptDate: 20170622
browser.urlbar.matchBuckets: general:5,suggestion:Infinity
browser.urlbar.placeholderName: Google
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extensions.formautofill.creditCards.used: 3
extensions.formautofill.firstTimeUse: false
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font.internaluseonly.changed: false
media.benchmark.vp9.fps: 271
media.benchmark.vp9.versioncheck: 5
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media.gmp-manager.lastCheck: 1549656325
media.gmp-widevinecdm.abi: x86_64-gcc3
media.gmp-widevinecdm.lastUpdate: 1543329936
media.gmp-widevinecdm.version: 4.10.1196.0
media.gmp.storage.version.observed: 1
network.cookie.prefsMigrated: true
network.predictor.cleaned-up: true
network.trr.experimentalRollout: -4
places.database.lastMaintenance: 1549358735
places.database.migrateV48Frecencies: true
places.history.expiration.transient_current_max_pages: 135359
plugin.disable_full_page_plugin_for_types: application/pdf
plugin.importedState: true
plugins.ctprollout.cohort: test
plugins.ctprollout.cohortSample: 0.320862
print.print_bgcolor: false
print.print_bgimages: false
print.print_duplex: 71303424
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print.printer__.print_edge_top: 0
print.printer__.print_evenpages: true
print.printer__.print_footercenter:
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print.printer__.print_footerright: &D
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print.printer__.print_headerright: &U
print.printer__.print_in_color: true
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print.printer__.print_scaling: 1.00
print.printer__.print_shrink_to_fit: true
print.printer__.print_to_file: false
print.printer__.print_unwriteable_margin_bottom: 17
print.printer__.print_unwriteable_margin_left: 17
print.printer__.print_unwriteable_margin_right: 17
print.printer__.print_unwriteable_margin_top: 17
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print.printer_SFO7-Folsom.print_scaling: 1.00
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print.printer_SFO7-Folsom.print_unwriteable_margin_left: 17
print.printer_SFO7-Folsom.print_unwriteable_margin_right: 17
print.printer_SFO7-Folsom.print_unwriteable_margin_top: 17
privacy.cpd.offlineApps: true
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services.sync.lastPing: 1549887062
services.sync.lastSync: Mon Feb 11 2019 11:16:22 GMT-0800 (Pacific Standard Time)
signon.debug: true
signon.importedFromSqlite: true
storage.vacuum.last.index: 0
storage.vacuum.last.places.sqlite: 1543636000

Important Locked Preferences

Places Database

JavaScript

Incremental GC: true

Accessibility

Activated: false
Prevent Accessibility: 0

Library Versions

NSPR
Expected minimum version: 4.20
Version in use: 4.20

NSS
Expected minimum version: 3.42
Version in use: 3.42

NSSSMIME
Expected minimum version: 3.42
Version in use: 3.42

NSSSSL
Expected minimum version: 3.42
Version in use: 3.42

NSSUTIL
Expected minimum version: 3.42
Version in use: 3.42

Sandbox

Content Process Sandbox Level: 3
Effective Content Process Sandbox Level: 3

Internationalization & Localization

Application Settings
Requested Locales: ["en-US"]
Available Locales: ["en-US"]
App Locales: ["en-US"]
Regional Preferences: ["en"]
Default Locale: "en-US"
Operating System
System Locales: ["en"]
Regional Preferences: ["en"]

mconley, are you aware of changes in 66 that could cause this?

Hm, very strange. Your content processes definitely don't seem very happy in that screenshot. :/

Do you experience this if you restart with your add-ons disabled? (Help > Restart with Add-ons Disabled)

I will try that Mike, stay tuned.

closing this one, susheel left

Hah, I'm still here Tim, but yes, I haven't been able to reproduce this, though note I've moved on to Nightly. I have a odd feeling it had to do with all the pinned tabs I had. I'll re-open if I can reproduce.