User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:67.0) Gecko/20100101 Firefox/67.0

Steps to reproduce:

open a link in a tab and switch to another tab. Then I return to back the tab

Actual results:

The page reloads from blank and takes time/cpu. This happens on all open tabs that I opened previously and I switch back to them. Very annoying..

Expected results:

Nothing! Just returning to my previously opened tab...

jheffez,
Could you please attach a results of about:support (Help –> Troubleshooting Information)?

Hi jheffez,

Is this something new you experience or it is an older bug you just reported?
It would be worth trying out a new profile or safe mode, custom settings and add-ons might also cause issues.

Please try it out with safe mode and a new profile if needed, here are the instructions for them:

Safe mode: https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode.
New Clean Profile: https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

Don't forget to attach the about:support results requested in Comment 1!
Thanks

(In reply to Alice0775 White from comment #1)

jheffez,
Could you please attach a results of about:support (Help –> Troubleshooting Information)?

Application Basics

Name: Firefox
Version: 67.0
Build ID: 20190516215225
Update Channel: release
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:67.0) Gecko/20100101 Firefox/67.0
OS: Windows_NT 10.0
Launcher Process: Disabled forcibly
Multiprocess Windows: 1/1 Enabled by default
Web Content Processes: 7/8
Enterprise Policies: Inactive
Google Location Service Key: Found
Google Safebrowsing Key: Found
Mozilla Location Service Key: Found
Safe Mode: false

Crash Reports

All Crash Reports Firefox Features

Name: Firefox Monitor
Version: 3.0
ID: fxmonitor@mozilla.org

Name: Firefox Screenshots
Version: 37.1.0
ID: screenshots@mozilla.org

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

Name: Web Compat
Version: 4.0.0
ID: webcompat@mozilla.org

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

Extensions

Name: AutocopySelection2Clipboard
Version: 3.3.0
Enabled: true
ID: autocopyselection2clipboard@dook

Name: Dark Reader
Version: 4.7.12
Enabled: true
ID: addon@darkreader.org

Name: FoxyProxy Standard
Version: 6.3
Enabled: true
ID: foxyproxy@eric.h.jung

Name: LastPass: Free Password Manager
Version: 4.28.0.4
Enabled: true
ID: support@lastpass.com

Name: Tab Reloader (page auto refresh)
Version: 0.2.5
Enabled: true
ID: jid0-bnmfwWw2w2w4e4edvcdDbnMhdVg@jetpack

Name: uBlock Origin
Version: 1.19.6
Enabled: true
ID: uBlock0@raymondhill.net

Security Software

Type: Bitdefender Antivirus Free Antimalware

Type: Bitdefender Antivirus Free Antimalware

Type: Windows Firewall

Graphics

Features
Compositing: Direct3D 11 (Advanced Layers)
asyncPanZoom: wheel input enabled; scrollbar drag enabled; keyboard enabled; autoscroll enabled
webgl1WSIInfo: EGL_VENDOR: Google Inc. (adapter LUID: 0000000000007f5c) EGL_VERSION: 1.4 (ANGLE 2.1.0.eff6bfdb1db9) 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 Family Direct3D11 vs_5_0 ps_5_0)
WebGL 1 Driver Version: OpenGL ES 2.0 (ANGLE 2.1.0.eff6bfdb1db9)
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_disjoint_timer_query EXT_float_blend EXT_frag_depth EXT_shader_texture_lod EXT_sRGB EXT_texture_filter_anisotropic 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: 0000000000007f5c) EGL_VERSION: 1.4 (ANGLE 2.1.0.eff6bfdb1db9) 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 Family Direct3D11 vs_5_0 ps_5_0)
WebGL 2 Driver Version: OpenGL ES 3.0 (ANGLE 2.1.0.eff6bfdb1db9)
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_disjoint_timer_query EXT_float_blend EXT_texture_filter_anisotropic 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
Off Main Thread Painting Enabled: true
Off Main Thread Painting Worker Count: 3
Target Frame Rate: 60
DirectWrite: true (10.0.17763.168)
GPU #1
Active: Yes
Description: Intel(R) HD Graphics Family
Vendor ID: 0x8086
Device ID: 0x0a16
Driver Version: 20.19.15.5058
Driver Date: 8-16-2018
Drivers: igdumdim64 igd10iumd64 igd10iumd64 igd12umd64 igdumdim32 igd10iumd32 igd10iumd32 igd12umd32
Subsys ID: 05de1028
RAM: Unknown

Diagnostics
AzureCanvasBackend: direct2d 1.1
AzureCanvasBackend (UI Process): skia
AzureContentBackend: direct2d 1.1
AzureContentBackend (UI Process): skia
AzureFallbackCanvasBackend (UI Process): cairo
GPUProcessPid: 364
ClearType Parameters: \.\DISPLAY1 [ Gamma: 1.8 Pixel Structure: RGB ClearType Level: 100 Enhanced Contrast: 50 ] \.\DISPLAY2 [ 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
WEBRENDER_QUALIFIED:
blocked by env: Has battery

Media

Audio Backend: wasapi
Max Channels: 2
Preferred Sample Rate: 48000
Output Devices
Name: Group
Digital Audio (HDMI) (High Definition Audio Device): HDAUDIO\FUNC_01&VEN_8086&DEV_2807&SUBSYS_80860101&REV_1000\4&1448f9e9&0&0001
Digital Output (BONGO):
Digital Audio (HDMI) (High Definition Audio Device): HDAUDIO\FUNC_01&VEN_8086&DEV_2807&SUBSYS_80860101&REV_1000\4&1448f9e9&0&0001
Digital Audio (HDMI) (High Definition Audio Device): HDAUDIO\FUNC_01&VEN_8086&DEV_2807&SUBSYS_80860101&REV_1000\4&1448f9e9&0&0001
Internal AUX Jack (High Definition Audio Device): HDAUDIO\FUNC_01&VEN_10EC&DEV_0292&SUBSYS_102805DE&REV_1000\4&364fe165&0&0001
Speakers (High Definition Audio Device): HDAUDIO\FUNC_01&VEN_10EC&DEV_0292&SUBSYS_102805DE&REV_1000\4&364fe165&0&0001
Speakers (High Definition Audio Device): HDAUDIO\FUNC_01&VEN_10EC&DEV_0292&SUBSYS_102805DE&REV_1000\4&364fe165&0&0001
:
Speakers / Headphones (Realtek High Definition Audio): HDAUDIO\FUNC_01&VEN_10EC&DEV_0292&SUBSYS_102805DE&REV_1000\4&364fe165&0&0001
Input Devices
Name: Group
Microphone (High Definition Audio Device): HDAUDIO\FUNC_01&VEN_10EC&DEV_0292&SUBSYS_102805DE&REV_1000\4&364fe165&0&0001
Internal AUX Jack (High Definition Audio Device): HDAUDIO\FUNC_01&VEN_8086&DEV_2807&SUBSYS_80860101&REV_1000\4&1448f9e9&0&0001
Microphone (High Definition Audio Device): HDAUDIO\FUNC_01&VEN_10EC&DEV_0292&SUBSYS_102805DE&REV_1000\4&364fe165&0&0001
Internal AUX Jack (High Definition Audio Device): HDAUDIO\FUNC_01&VEN_10EC&DEV_0292&SUBSYS_102805DE&REV_1000\4&364fe165&0&0001
Internal AUX Jack (High Definition Audio Device): HDAUDIO\FUNC_01&VEN_8086&DEV_2807&SUBSYS_80860101&REV_1000\4&1448f9e9&0&0001
Microphone Array (Realtek High Definition Audio): HDAUDIO\FUNC_01&VEN_10EC&DEV_0292&SUBSYS_102805DE&REV_1000\4&364fe165&0&0001
Stereo Mix (Realtek High Definition Audio): HDAUDIO\FUNC_01&VEN_10EC&DEV_0292&SUBSYS_102805DE&REV_1000\4&364fe165&0&0001
Jack Mic (Realtek High Definition Audio): HDAUDIO\FUNC_01&VEN_10EC&DEV_0292&SUBSYS_102805DE&REV_1000\4&364fe165&0&0001
Internal AUX Jack (High Definition Audio Device): HDAUDIO\FUNC_01&VEN_8086&DEV_2807&SUBSYS_80860101&REV_1000\4&1448f9e9&0&0001

Important Modified Preferences

browser.cache.disk.capacity: 1048576
browser.cache.disk.filesystem_reported: 1
browser.sessionstore.upgradeBackup.latestBuildID: 20190516215225
browser.startup.homepage_override.buildID: 20190516215225
browser.startup.homepage_override.mstone: 67.0
browser.tabs.warnOnClose: false
browser.urlbar.placeholderName: Google
browser.urlbar.timesBeforeHidingSuggestionsHint: 0
dom.push.userAgentID: db00999e486b4b398e2ebc572c38bc3d
extensions.lastAppVersion: 67.0
gfx.crash-guard.status.wmfvpxvideo: 2
gfx.crash-guard.wmfvpxvideo.appVersion: 67.0
gfx.crash-guard.wmfvpxvideo.deviceID: 0x0a16
gfx.crash-guard.wmfvpxvideo.driverVersion: 20.19.15.5058
layers.mlgpu.sanity-test-failed: false
media.gmp-gmpopenh264.abi: x86_64-msvc-x64
media.gmp-gmpopenh264.lastUpdate: 1559213255
media.gmp-gmpopenh264.version: 1.8.1
media.gmp-manager.buildID: 20190516215225
media.gmp-manager.lastCheck: 1559213254
media.gmp-widevinecdm.abi: x86_64-msvc-x64
media.gmp-widevinecdm.lastUpdate: 1559213257
media.gmp-widevinecdm.version: 4.10.1146.0
media.gmp.storage.version.observed: 1
media.hardware-video-decoding.failed: false
network.dns.disablePrefetch: true
network.http.speculative-parallel-limit: 0
network.predictor.cleaned-up: true
network.predictor.enabled: false
network.prefetch-next: false
places.history.expiration.transient_current_max_pages: 113976
plugin.disable_full_page_plugin_for_types: application/pdf
privacy.sanitize.pending: [{"id":"newtab-container","itemsToClear":[],"options":{}}]
security.remote_settings.intermediates.checked: 1559213255
security.sandbox.content.tempDirSuffix: {9fd5b224-d623-4cae-b1db-c323c6144ba8}
security.sandbox.plugin.tempDirSuffix: {a0b9c2ab-bb57-43e8-98b6-e6f12f0729ee}
services.sync.declinedEngines:
signon.importedFromSqlite: true
ui.osk.debug.keyboardDisplayReason: IKPOS: Touch screen not found.

Important Locked Preferences

Places Database

JavaScript

Incremental GC: true

Accessibility

Activated: false
Prevent Accessibility: 0
Accessible Handler Used: true
Accessibility Instantiator:

Library Versions

NSPR
Expected minimum version: 4.21
Version in use: 4.21

NSS
Expected minimum version: 3.43
Version in use: 3.43

NSSSMIME
Expected minimum version: 3.43
Version in use: 3.43

NSSSSL
Expected minimum version: 3.43
Version in use: 3.43

NSSUTIL
Expected minimum version: 3.43
Version in use: 3.43

Sandbox

Content Process Sandbox Level: 5
Effective Content Process Sandbox Level: 5

Internationalization & Localization

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

(In reply to Timea Babos from comment #2)

Hi jheffez,

Is this something new you experience or it is an older bug you just reported?
It would be worth trying out a new profile or safe mode, custom settings and add-ons might also cause issues.

Please try it out with safe mode and a new profile if needed, here are the instructions for them:

Safe mode: https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode.
New Clean Profile: https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

Don't forget to attach the about:support results requested in Comment 1!
Thanks

This is a new issue I noticed since FF 67. I tried the clean profile. same problem.

Can you reproduce with browser.tabs.unloadOnLowMemory set to false in about:config? How much memory does your system have?

(In reply to Dão Gottwald [::dao] from comment #5)

Can you reproduce with browser.tabs.unloadOnLowMemory set to false in about:config? How much memory does your system have?

Hi Dão, I configured as you suggested above. I think you're in the right direction. I noticed that today, before the config change, while my laptop is not stressed that the issue is not happening. It persists only while I strain my laptop's cpu and memory (8GB) by running certain apps. So it seems resource-related. I'l be able to find out later today when I run those apps how the config change works.

The thing is, the issue started with FF67. Prior FF (can't recall if 66 or 65) worked fine even during exact same stress times. Any ideas? Is it safe to leave browser.tabs.unloadOnLowMemory=False for now?

Sounds like this is working as intended then. Gabriele, can you confirm?

(In reply to jheffez from comment #6)

The thing is, the issue started with FF67. Prior FF (can't recall if 66 or 65) worked fine even during exact same stress times. Any ideas? Is it safe to leave browser.tabs.unloadOnLowMemory=False for now?

It's safe in the sense that you'll get pre-67 behavior, but this includes possibly crashing due to running out of memory.

(In reply to Dão Gottwald [::dao] from comment #7)

Sounds like this is working as intended then. Gabriele, can you confirm?

(In reply to jheffez from comment #6)

The thing is, the issue started with FF67. Prior FF (can't recall if 66 or 65) worked fine even during exact same stress times. Any ideas? Is it safe to leave browser.tabs.unloadOnLowMemory=False for now?

It's safe in the sense that you'll get pre-67 behavior, but this includes possibly crashing due to running out of memory.

Makes sense. I'll watch later today how the above setting impact and update the ticket. Thanks.

(In reply to Dão Gottwald [::dao] from comment #7)

Sounds like this is working as intended then. Gabriele, can you confirm?

Yes indeed.

(In reply to jheffez from comment #8)

Makes sense. I'll watch later today how the above setting impact and update the ticket. Thanks.

If you encounter the issue again with browser.tabs.unloadOnLowMemory set to true could you measure the current memory consumption? This would require navigating to about:memory, pressing the "Measure and save.." button and attaching the generated file to this bug.

Restored to original memory setting and created the attached

Thanks a lot! Looking at the report I'm seeing 17 low-memory events so you were running out of memory at the time this happened; that's why the mechanism kicked in and tried to unload some tabs to free up memory. How much memory does your machine have? Were other applications open besides Firefox? If you set browser.tabs.unloadOnLowMemory to false do tabs crash from time to time?

(In reply to jheffez from comment #6)

(In reply to Dão Gottwald [::dao] from comment #5)

Can you reproduce with browser.tabs.unloadOnLowMemory set to false in about:config? How much memory does your system have?

Hi Dão, I configured as you suggested above. I think you're in the right direction. I noticed that today, before the config change, while my laptop is not stressed that the issue is not happening. It persists only while I strain my laptop's cpu and memory (8GB) by running certain apps. So it seems resource-related. I'l be able to find out later today when I run those apps how the config change works.

The thing is, the issue started with FF67. Prior FF (can't recall if 66 or 65) worked fine even during exact same stress times. Any ideas? Is it safe to leave browser.tabs.unloadOnLowMemory=False for now?

Hi jheffez ,
It seems that you do not have enough memory. You might increase the size of swap file in operating system, or better get more RAM. Your 8 GB of RAM and swap file is simply not enough for software you run.
Did your Firefox or other programs crashed before Firefox 67?

(In reply to Gabriele Svelto [:gsvelto] from comment #10)

(In reply to jheffez from comment #8)

Makes sense. I'll watch later today how the above setting impact and update the ticket. Thanks.

If you encounter the issue again with browser.tabs.unloadOnLowMemory set to true could you measure the current memory consumption? This would require navigating to about:memory, pressing the "Measure and save.." button and attaching the generated file to this bug.

The uploaded memory diagnostics meets the above.
I did not have this situation prior to FF67. Same laptop, same environment. With that, I will be more watchful to memory (last night I did not see the issue since I freed unneeded apps). It will take a few days so please don't close ticket in the meantime.
Thanks.

Today I saw the issue again. This time without taxing the laptop and task manager reports 1.6GB available ram and 1.5GB cache. also uploading current about:memory file.

Thanks, this is very helpful. Firefox is committing ~3GiB of memory so there should still be plenty available but total commit space has dipped below the 384MiB threshold 25 times. The only explanation is that something is committing memory without using it. It's an odd situation because Windows still has free memory available - as reported by the task manager - but it will refuse to allocate it.

I need to add more probes to the memory reports to figure out where that memory is being committed (though it might not be within Firefox). In the meantime you can disable unloading on your machine, Firefox will still try to reclaim memory when it detects a low memory scenario, just not as aggressively as with tab unloading.

(In reply to Gabriele Svelto [:gsvelto] from comment #16)

Thanks, this is very helpful. Firefox is committing ~3GiB of memory so there should still be plenty available but total commit space has dipped below the 384MiB threshold 25 times. The only explanation is that something is committing memory without using it. It's an odd situation because Windows still has free memory available - as reported by the task manager - but it will refuse to allocate it.

I need to add more probes to the memory reports to figure out where that memory is being committed (though it might not be within Firefox). In the meantime you can disable unloading on your machine, Firefox will still try to reclaim memory when it detects a low memory scenario, just not as aggressively as with tab unloading.

I'd like to point out that the issue started with FF67.
Thanks for looking into it Gabriele.

browser.tabs.unloadOnLowMemory makes Firefox completely unusable on a 2GB tablet, so I think this effort to improve performance on low end devices unfortunately achieves the complete opposite.
Btw for whatever reason it apparently also breaks infinite scrolling on reddit, where it's suddenly impossible to scroll any further down and the bottom of the window starts flickering. I thought it's the shitty intel gpu, since it happened mostly after/before embedded videos, but after disabling browser.tabs.unloadOnLowMemory (because it was unloading things it definitely shouldn't) it stopped happening, though that requires further testing since it was rather intermittent.

I've confirmed the issue in bug 1558554 so duplicating against that one. The memory detection logic is being fooled by how windows reports available commit-space in the MEMORYSTATUSEX structure and when loading new pages it can sometimes incorrectly unload a tab even though there's still plenty of memory available.

So the scrolling issue on reddit mentioned in comment 18 is a WerRender issue (a much more severe variant of Bug 1541072), though browser.tabs.unloadOnLowMemory still makes it much easier to reproduce.