1366621 - horizontal lines in video

Status: RESOLVED WORKSFORME

(Core :: Graphics, defect, P3)

Description

[baz]

User Agent: Mozilla/5.0 (X11; Linux i686; rv:55.0) Gecko/20100101 Firefox/55.0
Build ID: 20170521100319

Steps to reproduce:

I open a tab on http://www.arte.tv/fr/direct/ (french & german tv) to watch a video.
 


Actual results:

What ever if it is in full screen or not, I see horizontal lines (1px height). 3 (or 4) regularly put on the video.
I changer the video resolution. I have this issue only with 360p (nothing with 240 ou 720p) 


Expected results:

The expect result is: a clean image, no horizontal lines.

I can't make a screen copy because when I stop the video, the image is correct, no line.

Comment 1

[Loic]

Could you attach some screenshots of the issue, please.

In addition, type about:support in the location bar and paste the section "graphics".

Does it happen with FF53?

Comment 2

[Loic]

NB: just press "Print Screen" on your keyboard to take a screenshot of the video without stopping it.

Comment 3

[baz]

Attachment: Screenshot using FF 55

Comment 4

[baz]

Attachment: Screenshot using FF 53

Comment 5

[baz]

I had 2 screenshots using both FF55 and FF53.

I add that it appends using the parameter 360p.

Comment 6

[baz]

To answer your question:
As you can see on the screenshots, it does not happen in FF53.

Here is a copy/paste of about:support (partly):

Accélération graphique
Fonctionnalités
Composition	Basic
Zoom/Panoramique asynchrones	entrée molette activée; faire glisser les barres de défilement
Pilote WebGL 1 - Informations WSI	GLX 1.4
GLX_VENDOR(client): Mesa Project and SGI
GLX_VENDOR(server): SGI
Extensions: GLX_ARB_create_context GLX_ARB_create_context_profile GLX_ARB_create_context_robustness GLX_ARB_fbconfig_float GLX_ARB_framebuffer_sRGB GLX_ARB_get_proc_address GLX_ARB_multisample GLX_EXT_import_context GLX_EXT_visual_info GLX_EXT_visual_rating GLX_EXT_fbconfig_packed_float GLX_EXT_framebuffer_sRGB GLX_EXT_create_context_es2_profile GLX_EXT_create_context_es_profile GLX_MESA_copy_sub_buffer GLX_MESA_multithread_makecurrent GLX_MESA_query_renderer GLX_MESA_swap_control GLX_OML_swap_method GLX_OML_sync_control GLX_SGI_make_current_read GLX_SGI_swap_control GLX_SGI_video_sync GLX_SGIS_multisample GLX_SGIX_fbconfig GLX_SGIX_pbuffer GLX_SGIX_visual_select_group GLX_EXT_texture_from_pixmap GLX_INTEL_swap_event 
Pilote WebGL 1 - Rendu	Intel Open Source Technology Center -- Mesa DRI Intel(R) HD Graphics 520 (Skylake GT2) x86/MMX/SSE2
Pilote WebGL 1 - Version	3.0 Mesa 12.0.6
Pilote WebGL 1 - Extensions	GL_ARB_multisample GL_EXT_abgr GL_EXT_bgra GL_EXT_blend_color GL_EXT_blend_minmax GL_EXT_blend_subtract GL_EXT_copy_texture GL_EXT_polygon_offset GL_EXT_subtexture GL_EXT_texture_object GL_EXT_vertex_array GL_EXT_compiled_vertex_array GL_EXT_texture GL_EXT_texture3D GL_IBM_rasterpos_clip GL_ARB_point_parameters GL_EXT_draw_range_elements GL_EXT_packed_pixels GL_EXT_point_parameters GL_EXT_rescale_normal GL_EXT_separate_specular_color GL_EXT_texture_edge_clamp GL_SGIS_generate_mipmap GL_SGIS_texture_border_clamp GL_SGIS_texture_edge_clamp GL_SGIS_texture_lod GL_ARB_framebuffer_sRGB GL_ARB_multitexture GL_EXT_framebuffer_sRGB GL_IBM_multimode_draw_arrays GL_IBM_texture_mirrored_repeat GL_3DFX_texture_compression_FXT1 GL_ARB_texture_cube_map GL_ARB_texture_env_add GL_ARB_transpose_matrix GL_EXT_blend_func_separate GL_EXT_fog_coord GL_EXT_multi_draw_arrays GL_EXT_secondary_color GL_EXT_texture_env_add GL_EXT_texture_filter_anisotropic GL_EXT_texture_lod_bias GL_INGR_blend_func_separate GL_NV_blend_square GL_NV_light_max_exponent GL_NV_texgen_reflection GL_NV_texture_env_combine4 GL_S3_s3tc GL_SUN_multi_draw_arrays GL_ARB_texture_border_clamp GL_ARB_texture_compression GL_EXT_framebuffer_object GL_EXT_texture_compression_s3tc GL_EXT_texture_env_combine GL_EXT_texture_env_dot3 GL_MESA_window_pos GL_NV_packed_depth_stencil GL_NV_texture_rectangle GL_ARB_depth_texture GL_ARB_occlusion_query GL_ARB_shadow GL_ARB_texture_env_combine GL_ARB_texture_env_crossbar GL_ARB_texture_env_dot3 GL_ARB_texture_mirrored_repeat GL_ARB_window_pos GL_EXT_stencil_two_side GL_EXT_texture_cube_map GL_NV_depth_clamp GL_APPLE_packed_pixels GL_APPLE_vertex_array_object GL_ARB_draw_buffers GL_ARB_fragment_program GL_ARB_fragment_shader GL_ARB_shader_objects GL_ARB_vertex_program GL_ARB_vertex_shader GL_ATI_draw_buffers GL_ATI_texture_env_combine3 GL_ATI_texture_float GL_EXT_shadow_funcs GL_EXT_stencil_wrap GL_MESA_pack_invert GL_NV_primitive_restart GL_ARB_depth_clamp GL_ARB_fragment_program_shadow GL_ARB_half_float_pixel GL_ARB_occlusion_query2 GL_ARB_point_sprite GL_ARB_shading_language_100 GL_ARB_sync GL_ARB_texture_non_power_of_two GL_ARB_vertex_buffer_object GL_ATI_blend_equation_separate GL_EXT_blend_equation_separate GL_OES_read_format GL_ARB_color_buffer_float GL_ARB_pixel_buffer_object GL_ARB_texture_compression_rgtc GL_ARB_texture_float GL_ARB_texture_rectangle GL_EXT_packed_float GL_EXT_pixel_buffer_object GL_EXT_texture_compression_dxt1 GL_EXT_texture_compression_rgtc GL_EXT_texture_rectangle GL_EXT_texture_sRGB GL_EXT_texture_shared_exponent GL_ARB_framebuffer_object GL_EXT_framebuffer_blit GL_EXT_framebuffer_multisample GL_EXT_packed_depth_stencil GL_APPLE_object_purgeable GL_ARB_vertex_array_object GL_ATI_separate_stencil GL_EXT_draw_buffers2 GL_EXT_draw_instanced GL_EXT_gpu_program_parameters GL_EXT_texture_array GL_EXT_texture_integer GL_EXT_texture_sRGB_decode GL_EXT_timer_query GL_OES_EGL_image GL_ARB_copy_buffer GL_ARB_depth_buffer_float GL_ARB_draw_instanced GL_ARB_half_float_vertex GL_ARB_instanced_arrays GL_ARB_map_buffer_range GL_ARB_texture_rg GL_ARB_texture_swizzle GL_ARB_vertex_array_bgra GL_EXT_texture_swizzle GL_EXT_vertex_array_bgra GL_NV_conditional_render GL_AMD_conservative_depth GL_AMD_draw_buffers_blend GL_AMD_seamless_cubemap_per_texture GL_AMD_shader_stencil_export GL_ARB_ES2_compatibility GL_ARB_blend_func_extended GL_ARB_debug_output GL_ARB_draw_buffers_blend GL_ARB_draw_elements_base_vertex GL_ARB_explicit_attrib_location GL_ARB_fragment_coord_conventions GL_ARB_provoking_vertex GL_ARB_sample_shading GL_ARB_sampler_objects GL_ARB_seamless_cube_map GL_ARB_shader_stencil_export GL_ARB_shader_texture_lod GL_ARB_texture_cube_map_array GL_ARB_texture_gather GL_ARB_texture_multisample GL_ARB_texture_query_lod GL_ARB_texture_rgb10_a2ui GL_ARB_uniform_buffer_object GL_ARB_vertex_type_2_10_10_10_rev GL_EXT_provoking_vertex GL_EXT_texture_snorm GL_MESA_texture_signed_rgba GL_NV_texture_barrier GL_ARB_get_program_binary GL_ARB_robustness GL_ARB_separate_shader_objects GL_ARB_shader_bit_encoding GL_ARB_shader_precision GL_ARB_texture_compression_bptc GL_ARB_timer_query GL_ARB_transform_feedback2 GL_ARB_transform_feedback3 GL_ANGLE_texture_compression_dxt3 GL_ANGLE_texture_compression_dxt5 GL_ARB_compressed_texture_pixel_storage GL_ARB_conservative_depth GL_ARB_internalformat_query GL_ARB_map_buffer_alignment GL_ARB_shader_atomic_counters GL_ARB_shader_image_load_store GL_ARB_shading_language_420pack GL_ARB_shading_language_packing GL_ARB_texture_storage GL_ARB_transform_feedback_instanced GL_EXT_framebuffer_multisample_blit_scaled GL_EXT_transform_feedback GL_AMD_shader_trinary_minmax GL_ARB_ES3_compatibility GL_ARB_arrays_of_arrays GL_ARB_clear_buffer_object GL_ARB_compute_shader GL_ARB_copy_image GL_ARB_explicit_uniform_location GL_ARB_framebuffer_no_attachments GL_ARB_invalidate_subdata GL_ARB_program_interface_query GL_ARB_robust_buffer_access_behavior GL_ARB_shader_image_size GL_ARB_shader_storage_buffer_object GL_ARB_stencil_texturing GL_ARB_texture_query_levels GL_ARB_texture_storage_multisample GL_ARB_texture_view GL_ARB_vertex_attrib_binding GL_KHR_debug GL_KHR_robustness GL_KHR_texture_compression_astc_ldr GL_ARB_buffer_storage GL_ARB_clear_texture GL_ARB_internalformat_query2 GL_ARB_multi_bind GL_ARB_query_buffer_object GL_ARB_seamless_cubemap_per_texture GL_ARB_shader_draw_parameters GL_ARB_texture_mirror_clamp_to_edge GL_ARB_texture_stencil8 GL_ARB_vertex_type_10f_11f_11f_rev GL_EXT_shader_integer_mix GL_ARB_clip_control GL_ARB_conditional_render_inverted GL_ARB_cull_distance GL_ARB_derivative_control GL_ARB_get_texture_sub_image GL_ARB_pipeline_statistics_query GL_ARB_shader_texture_image_samples GL_ARB_texture_barrier GL_EXT_polygon_offset_clamp GL_KHR_context_flush_control GL_KHR_robust_buffer_access_behavior GL_ARB_shader_clock GL_EXT_shader_samples_identical 
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 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_astc WEBGL_compressed_texture_etc WEBGL_compressed_texture_s3tc WEBGL_debug_renderer_info WEBGL_debug_shaders WEBGL_depth_texture WEBGL_draw_buffers WEBGL_lose_context MOZ_WEBGL_lose_context MOZ_WEBGL_compressed_texture_s3tc MOZ_WEBGL_depth_texture
Pilote WebGL 2 - Informations WSI	GLX 1.4
GLX_VENDOR(client): Mesa Project and SGI
GLX_VENDOR(server): SGI
Extensions: GLX_ARB_create_context GLX_ARB_create_context_profile GLX_ARB_create_context_robustness GLX_ARB_fbconfig_float GLX_ARB_framebuffer_sRGB GLX_ARB_get_proc_address GLX_ARB_multisample GLX_EXT_import_context GLX_EXT_visual_info GLX_EXT_visual_rating GLX_EXT_fbconfig_packed_float GLX_EXT_framebuffer_sRGB GLX_EXT_create_context_es2_profile GLX_EXT_create_context_es_profile GLX_MESA_copy_sub_buffer GLX_MESA_multithread_makecurrent GLX_MESA_query_renderer GLX_MESA_swap_control GLX_OML_swap_method GLX_OML_sync_control GLX_SGI_make_current_read GLX_SGI_swap_control GLX_SGI_video_sync GLX_SGIS_multisample GLX_SGIX_fbconfig GLX_SGIX_pbuffer GLX_SGIX_visual_select_group GLX_EXT_texture_from_pixmap GLX_INTEL_swap_event 
Pilote WebGL 2 - Rendu	Intel Open Source Technology Center -- Mesa DRI Intel(R) HD Graphics 520 (Skylake GT2) x86/MMX/SSE2
Pilote WebGL 2 - Version	4.3 (Core Profile) Mesa 12.0.6
Pilote WebGL 2 - Extensions	GL_3DFX_texture_compression_FXT1 GL_AMD_conservative_depth GL_AMD_draw_buffers_blend GL_AMD_seamless_cubemap_per_texture GL_AMD_shader_stencil_export GL_AMD_shader_trinary_minmax GL_AMD_vertex_shader_layer GL_AMD_vertex_shader_viewport_index GL_ANGLE_texture_compression_dxt3 GL_ANGLE_texture_compression_dxt5 GL_APPLE_object_purgeable GL_ARB_ES2_compatibility GL_ARB_ES3_compatibility GL_ARB_arrays_of_arrays GL_ARB_base_instance GL_ARB_blend_func_extended GL_ARB_buffer_storage GL_ARB_clear_buffer_object GL_ARB_clear_texture GL_ARB_clip_control GL_ARB_compressed_texture_pixel_storage GL_ARB_compute_shader GL_ARB_conditional_render_inverted GL_ARB_conservative_depth GL_ARB_copy_buffer GL_ARB_copy_image GL_ARB_cull_distance GL_ARB_debug_output GL_ARB_depth_buffer_float GL_ARB_depth_clamp GL_ARB_derivative_control GL_ARB_direct_state_access GL_ARB_draw_buffers GL_ARB_draw_buffers_blend GL_ARB_draw_elements_base_vertex GL_ARB_draw_indirect GL_ARB_draw_instanced GL_ARB_explicit_attrib_location GL_ARB_explicit_uniform_location GL_ARB_fragment_coord_conventions GL_ARB_fragment_layer_viewport GL_ARB_fragment_shader GL_ARB_framebuffer_no_attachments GL_ARB_framebuffer_object GL_ARB_framebuffer_sRGB GL_ARB_get_program_binary GL_ARB_get_texture_sub_image GL_ARB_gpu_shader5 GL_ARB_gpu_shader_fp64 GL_ARB_half_float_pixel GL_ARB_half_float_vertex GL_ARB_instanced_arrays GL_ARB_internalformat_query GL_ARB_internalformat_query2 GL_ARB_invalidate_subdata GL_ARB_map_buffer_alignment GL_ARB_map_buffer_range GL_ARB_multi_bind GL_ARB_multi_draw_indirect GL_ARB_occlusion_query2 GL_ARB_pipeline_statistics_query GL_ARB_pixel_buffer_object GL_ARB_point_sprite GL_ARB_program_interface_query GL_ARB_provoking_vertex GL_ARB_query_buffer_object GL_ARB_robust_buffer_access_behavior GL_ARB_robustness GL_ARB_sample_shading GL_ARB_sampler_objects GL_ARB_seamless_cube_map GL_ARB_seamless_cubemap_per_texture GL_ARB_separate_shader_objects GL_ARB_shader_atomic_counters GL_ARB_shader_bit_encoding GL_ARB_shader_clock GL_ARB_shader_draw_parameters GL_ARB_shader_image_load_store GL_ARB_shader_image_size GL_ARB_shader_objects GL_ARB_shader_precision GL_ARB_shader_stencil_export GL_ARB_shader_storage_buffer_object GL_ARB_shader_subroutine GL_ARB_shader_texture_image_samples GL_ARB_shader_texture_lod GL_ARB_shading_language_420pack GL_ARB_shading_language_packing GL_ARB_stencil_texturing GL_ARB_sync GL_ARB_tessellation_shader GL_ARB_texture_barrier GL_ARB_texture_buffer_object GL_ARB_texture_buffer_object_rgb32 GL_ARB_texture_buffer_range GL_ARB_texture_compression_bptc GL_ARB_texture_compression_rgtc GL_ARB_texture_cube_map_array GL_ARB_texture_float GL_ARB_texture_gather GL_ARB_texture_mirror_clamp_to_edge GL_ARB_texture_multisample GL_ARB_texture_non_power_of_two GL_ARB_texture_query_levels GL_ARB_texture_query_lod GL_ARB_texture_rectangle GL_ARB_texture_rg GL_ARB_texture_rgb10_a2ui GL_ARB_texture_stencil8 GL_ARB_texture_storage GL_ARB_texture_storage_multisample GL_ARB_texture_swizzle GL_ARB_texture_view GL_ARB_timer_query GL_ARB_transform_feedback2 GL_ARB_transform_feedback3 GL_ARB_transform_feedback_instanced GL_ARB_uniform_buffer_object GL_ARB_vertex_array_bgra GL_ARB_vertex_array_object GL_ARB_vertex_attrib_64bit GL_ARB_vertex_attrib_binding GL_ARB_vertex_shader GL_ARB_vertex_type_10f_11f_11f_rev GL_ARB_vertex_type_2_10_10_10_rev GL_ARB_viewport_array GL_ATI_blend_equation_separate GL_ATI_texture_float GL_EXT_abgr GL_EXT_blend_equation_separate GL_EXT_draw_buffers2 GL_EXT_draw_instanced GL_EXT_framebuffer_blit GL_EXT_framebuffer_multisample GL_EXT_framebuffer_multisample_blit_scaled GL_EXT_framebuffer_sRGB GL_EXT_packed_depth_stencil GL_EXT_packed_float GL_EXT_pixel_buffer_object GL_EXT_polygon_offset_clamp GL_EXT_provoking_vertex GL_EXT_shader_integer_mix GL_EXT_shader_samples_identical GL_EXT_texture_array GL_EXT_texture_compression_dxt1 GL_EXT_texture_compression_rgtc GL_EXT_texture_compression_s3tc GL_EXT_texture_filter_anisotropic GL_EXT_texture_integer GL_EXT_texture_sRGB GL_EXT_texture_sRGB_decode GL_EXT_texture_shared_exponent GL_EXT_texture_snorm GL_EXT_texture_swizzle GL_EXT_timer_query GL_EXT_transform_feedback GL_EXT_vertex_array_bgra GL_IBM_multimode_draw_arrays GL_KHR_context_flush_control GL_KHR_debug GL_KHR_robust_buffer_access_behavior GL_KHR_robustness GL_KHR_texture_compression_astc_ldr GL_MESA_pack_invert GL_MESA_texture_signed_rgba GL_NV_conditional_render GL_NV_depth_clamp GL_NV_packed_depth_stencil GL_NV_texture_barrier GL_OES_EGL_image GL_OES_read_format GL_S3_s3tc
WebGL 2 - Extensions	EXT_color_buffer_float EXT_texture_filter_anisotropic EXT_disjoint_timer_query MOZ_debug OES_texture_float_linear WEBGL_compressed_texture_astc WEBGL_compressed_texture_etc WEBGL_compressed_texture_s3tc WEBGL_debug_renderer_info WEBGL_debug_shaders WEBGL_lose_context MOZ_WEBGL_lose_context MOZ_WEBGL_compressed_texture_s3tc
Backend audio	pulse
GPU 1
Actif	Oui
Description	Intel Open Source Technology Center -- Mesa DRI Intel(R) HD Graphics 520 (Skylake GT2) x86/MMX/SSE2
ID du vendeur	Intel Open Source Technology Center
ID du périphérique	Mesa DRI Intel(R) HD Graphics 520 (Skylake GT2) x86/MMX/SSE2
Version du pilote	3.0 Mesa 12.0.6
Diagnostics
AzureCanvasAccelerated	0
AzureCanvasBackend	skia
AzureContentBackend	skia
AzureFallbackCanvasBackend	none
CairoUseXRender	0
Journal des décisions
HW_COMPOSITING	
blocked by default: Acceleration blocked by platform
OPENGL_COMPOSITING	
unavailable by default: Hardware compositing is disabled
WEBRENDER	
opt-in by default: WebRender is an opt-in feature

Comment 7

[Loic]

I tried with 55 on Win 7, but I can't reproduce it and I suspect it's specific to the Linux version.
As it works in 53 but not in 55, it's probably a recent regression.

Could you run the tool mozregression to narrow down a regression range in 55.
See http://mozilla.github.io/mozregression/ for details.
Run the command "mozregression --good=53" then for each nightly build downloaded, make the test and enter if the build is good or bad. After the run, paste here the final pushlog.

Comment 8

[baz]

I installed mozregression and I made lots of installs and tests ! ;-)
and it is not finished yet... I will continue tomorrow.

Comment 9

[baz]

Finally:
30:43.68 INFO: No more inbound revisions, bisection finished.
30:43.68 INFO: Last good revision: 3460a22b7c62160047431f88eaca952f8a0e0624
30:43.68 INFO: First bad revision: 6e02d48ef1226c6f8c7504c05dac113794d65f07
30:43.68 INFO: Pushlog:
https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=3460a22b7c62160047431f88eaca952f8a0e0624&tochange=6e02d48ef1226c6f8c7504c05dac113794d65f07

30:45.60 INFO: Looks like the following bug has the  changes which introduced the regression:
https://bugzilla.mozilla.org/show_bug.cgi?id=1323284

(I hope my tests were correct, as the bug -the horizontal lines- do not appear directly when the video starts but suddenly after a variable time). In addition I add that when the bug is visible, it is in every resolution and is not limited to 360p as I wrote before).

Comment 10

[Anthony Jones (:ajones, :kentuckyfriedtakahe, :k17e)]

Given that it is regressed by a graphics change, I'm going to assume it is a graphics issue.

Comment 11

[Lee Salzman [:lsalzman]]

(In reply to Anthony Jones (:kentuckyfriedtakahe, :k17e) from comment #10)
> Given that it is regressed by a graphics change, I'm going to assume it is a
> graphics issue.

Disabling GL acceleration by default on Linux was not really a graphics change, per se, but a policy decision. Given that GL acceleration was buggy and crashy in general, we couldn't allow it on in its current state. So it's just now going through the fallback software pathways. This may expose preexisting bugs in code paths that were not necessarily graphics related, but may have in some form or another escaped scrutiny because "it seemed to work" with GL acceleration on.

So I would still appreciate if A/V guys can look into it just to ensure there is nothing weird going on in their neck of the woods with software decode.

Comment 12

[Jean-Yves Avenard [:jya]]

On linux, the decoder is common, regardless of using accelerated layers or not. It uses libavcodec which output a YUV420 software buffer.

From that point on, the image (with software YUV buffer) is passed to the compositor.

Seeing that the lines are only seen without GL acceleration, that leaves only the gfx/compositor as culprit unfortunately.

The A/V stack is 100% the same regardless of having GL acceleration or not, only gfx is different.

Comment 13

[Anthony Jones (:ajones, :kentuckyfriedtakahe, :k17e)]

(In reply to Lee Salzman [:lsalzman] from comment #11)
> So I would still appreciate if A/V guys can look into it just to ensure
> there is nothing weird going on in their neck of the woods with software
> decode.

We use a software path on Linux so while nothing in life is guaranteed, this is most likely a graphics issue.

Comment 14

[Lee Salzman [:lsalzman]]

I tried several ways to reproduce this on my end, but was unable to. E10s on/off, fullscreen on/off, all resolutions, and they all worked without any apparent visual artifacts.

baz, what version(s) of libavcodec do you have installed?

Comment 15

[baz]

I have on idea, how could i check ?

Comment 16

[mirh]

If you are stuck on mesa 12.0.6, and you are on ubuntu, then you are either on 16.04 or 16.10. That when fully updated have either 2.8.11 or 3.0.7. 

I think "apt-show-versions ffmpeg" should do it?

Comment 17

[Lee Salzman [:lsalzman]]

(In reply to baz from comment #15)
> I have on idea, how could i check ?

If you are on Debian or Ubuntu, you could use: aptitude versions libavcodec

Comment 18

[baz]

I use Ubuntu 16.04 (32 bits)

@mirh: "ffmpeg:i386 not installed"

@Lee: the result of "aptitude versions libavcodec" is
p   7:2.8.6-1ubuntu2                              xenial                    500 
p   7:2.8.11-0ubuntu0.16.04.1                     xenial-security,xenial-up 500 

Paquet libavcodec-extra :
p A 7:2.8.6-1ubuntu2                              xenial                    500 
i A 7:2.8.11-0ubuntu0.16.04.1                     xenial-security,xenial-up 500 

Paquet libavcodec-ffmpeg-extra56 :
p A 7:2.8.6-1ubuntu2                              xenial                    500 
i A 7:2.8.11-0ubuntu0.16.04.1                     xenial-security,xenial-up 500 

Paquet libavcodec-ffmpeg56 :
p   7:2.8.6-1ubuntu2                              xenial                    500 
p   7:2.8.11-0ubuntu0.16.04.1                     xenial-security,xenial-up 500

Comment 19

[baz]

I don't have this problem anymore.
I currently use FF 57.0a1 on Ubuntu 16.04 (32 bits).

Comment 20

[mirh]

Firefox improvement or upstream?
Does it still happen on FF 55?

Comment 21

[baz]

Don't have it also on FF 55 ...

Comment 22

[Loic]

Let's close it as the OP is not able to reproduce the issue anymore.