Sandboxed Firefox gives troubles reproducing videos

[taonik]

I'm using Firefox 58.x, from the user prospective everything works fine, except for the fact videos (e.g. Youtube) are continuously interrupted.

oz logs show:

1. an issue with pyOpenGL (missing accelerate module),
2. ldconfig is not accessible inside the sandbox,
3. there are some problems with the encoding process.

oz logs:

15:08:01 ▶ INFO 063 [firefox] Hostname set to (firefox.local)
15:08:01 ▶ INFO 065 [firefox] xpra work dir is /home/user/.Xoz/firefox
15:08:01 ▶ INFO 066 [firefox] Starting xpra server
15:08:01 ▶ DEBU 067 [firefox] (xpra-server) I /usr/bin/xpra [/usr/bin/xpra --no-daemon --mmap --no-sharing --bell --system-tray --xsettings --cursors --encoding=rgb --clipboard --no-microphone --no-speaker --no-notifications --no-mdns --input-method=keep --bind=/home/user/.Xoz/firefox --socket-dir=/home/user/.Xoz/firefox start :0]
15:08:01 ▶ DEBU 068 [firefox] (xpra-server) Warning: invalid option: 'html'
15:08:01 ▶ DEBU 06e [firefox] (xpra-server) X.Org X Server 1.19.2
15:08:01 ▶ DEBU 06f [firefox] (xpra-server) Release Date: 2017-03-02
15:08:01 ▶ DEBU 070 [firefox] (xpra-server) X Protocol Version 11, Revision 0
15:08:01 ▶ DEBU 071 [firefox] (xpra-server) Build Operating System: Linux 4.9.0-4-amd64 x86_64 Debian
15:08:01 ▶ DEBU 072 [firefox] (xpra-server) Current Operating System: Linux firefox Linux 4.9.0-4-amd64 x86_64 #1 SMP Thu Feb 8 20:01:16 UTC 2018 x86_64
15:08:01 ▶ DEBU 073 [firefox] (xpra-server) Kernel command line: root=/dev/mapper/dmroot ro nomodeset console=hvc0
15:08:01 ▶ DEBU 074 [firefox] (xpra-server) Build Date: 16 October 2017  08:19:45AM
15:08:01 ▶ DEBU 075 [firefox] (xpra-server) xorg-server 2:1.19.2-1+deb9u2 (https://www.debian.org/support) 
15:08:01 ▶ DEBU 076 [firefox] (xpra-server) Current version of pixman: 0.34.0
15:08:01 ▶ DEBU 077 [firefox] (xpra-server) 	Before reporting problems, check http://wiki.x.org
15:08:01 ▶ DEBU 078 [firefox] (xpra-server) 	to make sure that you have the latest version.
15:08:01 ▶ DEBU 079 [firefox] (xpra-server) Markers: (--) probed, (**) from config file, (==) default setting,
15:08:01 ▶ DEBU 07a [firefox] (xpra-server) 	(++) from command line, (!!) notice, (II) informational,
15:08:01 ▶ DEBU 07b [firefox] (xpra-server) 	(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
15:08:01 ▶ DEBU 07c [firefox] (xpra-server) (++) Log file: "/home/user/.xpra/Xorg.:0.log", Time: Wed Mar 21 15:08:01 2018
15:08:01 ▶ DEBU 07d [firefox] (xpra-server) (++) Using config file: "/etc/xpra/xorg.conf"
15:08:01 ▶ DEBU 07e [firefox] (xpra-server) (==) Using system config directory "/usr/share/X11/xorg.conf.d"
15:08:01 ▶ DEBU 07f [firefox] (xpra-server) 2018-03-21 15:08:01,799 created unix domain socket: /home/user/.Xoz/firefox/firefox-0
15:08:03 ▶ DEBU 080 [firefox] (xpra-server) 2018-03-21 15:08:03,470 Warning: all the compressors are disabled,
15:08:03 ▶ DEBU 081 [firefox] (xpra-server) 2018-03-21 15:08:03,470  unless you have a gigabit connection or better, performance will suffer
15:08:04 ▶ DEBU 082 [firefox] (xpra-server) 2018-03-21 15:08:04,810 Failed to launch ldconfig -p: [Errno 2] No such file or directory
15:08:05 ▶ DEBU 083 [firefox] (xpra-server) 2018-03-21 15:08:05,803 xpra X11 version 0.17.6-r14322
15:08:05 ▶ DEBU 084 [firefox] (xpra-server) 2018-03-21 15:08:05,804  running with pid 9 on Linux
15:08:05 ▶ DEBU 085 [firefox] (xpra-server) 2018-03-21 15:08:05,804  on display :0
15:08:05 ▶ DEBU 086 [firefox] (xpra-server) 2018-03-21 15:08:05,949 xpra is ready.
15:08:05 ▶ INFO 087 [firefox] XPRA started
15:08:05 ▶ INFO 088 oz-init (firefox) is ready
15:08:05 ▶ INFO 089 [firefox] Run program message received: &{Args:[] Pwd:/home/user Path:/usr/lib/firefox/firefox}
15:08:05 ▶ INFO 08a [firefox] (xpra-client-stderr) I /usr/bin/xpra [/usr/bin/xpra --no-daemon --mmap --no-sharing --bell --system-tray --xsettings --cursors --encoding=rgb --clipboard --no-microphone --no-speaker --no-notifications --title=@title@ --compress=0 --no-keyboard-sync --no-tray --socket-dir=/home/user/.Xoz/firefox attach :0]
15:08:06 ▶ INFO 08b [firefox] (xpra-client-stderr) Warning: invalid option: 'html'
15:08:06 ▶ INFO 08c [firefox] (xpra-client-stderr) 2018-03-21 15:08:06,910 Warning: all the compressors are disabled,
15:08:06 ▶ INFO 08d [firefox] (xpra-client-stderr) 2018-03-21 15:08:06,911  unless you have a gigabit connection or better, performance will suffer
15:08:06 ▶ INFO 08e [firefox] (xpra-client-stderr) 2018-03-21 15:08:06,912 Xpra gtk2 client version 0.17.6-r14322
15:08:06 ▶ INFO 08f [firefox] (xpra-client-stderr) 2018-03-21 15:08:06,913  running on Linux debian 9.4
15:08:08 ▶ INFO 090 [firefox] (xpra-client-stderr) 2018-03-21 15:08:08,028 PyOpenGL warning: missing accelerate module
15:08:08 ▶ INFO 091 [firefox] (xpra-client-stderr) 2018-03-21 15:08:08,030 OpenGL support is missing:
15:08:08 ▶ INFO 092 [firefox] (xpra-client-stderr) 2018-03-21 15:08:08,030  vendor 'VMware, Inc.' is blacklisted!
15:08:08 ▶ DEBU 093 [firefox] (xpra-server) 2018-03-21 15:08:08,060 New unix-domain connection received on /home/user/.Xoz/firefox/firefox-0
15:08:08 ▶ DEBU 094 [firefox] (xpra-server) 2018-03-21 15:08:08,061 New unix-domain connection received on /home/user/.Xoz/firefox/firefox-0
15:08:08 ▶ DEBU 095 [firefox] (xpra-server) 2018-03-21 15:08:08,069 Connection lost
15:08:08 ▶ INFO 096 [firefox] (xpra-client-stderr) 2018-03-21 15:08:08,070  detected keyboard: rules=evdev, model=pc105, layout=us
15:08:08 ▶ INFO 097 [firefox] (xpra-client-stderr) 2018-03-21 15:08:08,072  desktop size is 1368x768 with 1 screen:
15:08:08 ▶ INFO 098 [firefox] (xpra-client-stderr) 2018-03-21 15:08:08,073   :0.0 (361x203 mm - DPI: 96x96)
15:08:08 ▶ INFO 099 [firefox] (xpra-client-stderr) 2018-03-21 15:08:08,074     monitor 1 (362x203 mm - DPI: 95x96)
15:08:08 ▶ DEBU 09a [firefox] (xpra-server) 2018-03-21 15:08:08,152 Handshake complete; enabling connection
15:08:08 ▶ DEBU 09b [firefox] (xpra-server) 2018-03-21 15:08:08,222 Python/Gtk2 Linux debian 9.4 client version 0.17.6-r14322
15:08:08 ▶ DEBU 09c [firefox] (xpra-server) 2018-03-21 15:08:08,222  connected from 'work' as 'user'
15:08:08 ▶ DEBU 09d [firefox] (xpra-server) 2018-03-21 15:08:08,223  mmap is enabled using 256MB area in /home/user/.Xoz/firefox/xpra.SG4nDj.mmap
15:08:08 ▶ DEBU 09e [firefox] (xpra-server) 2018-03-21 15:08:08,234  client root window size is 1368x768 with 1 display:
15:08:08 ▶ DEBU 09f [firefox] (xpra-server) 2018-03-21 15:08:08,234   :0.0 (361x203 mm - DPI: 96x96)
15:08:08 ▶ DEBU 0a0 [firefox] (xpra-server) 2018-03-21 15:08:08,235     monitor 1 (362x203 mm - DPI: 95x96)
15:08:08 ▶ DEBU 0a1 [firefox] (xpra-server) 2018-03-21 15:08:08,340 server virtual display now set to 1400x900 (best match for 1368x768)
15:08:08 ▶ DEBU 0a2 [firefox] (xpra-server) 2018-03-21 15:08:08,341 setting key repeat rate from client: 660ms delay / 40ms interval
15:08:08 ▶ DEBU 0a3 [firefox] (xpra-server) 2018-03-21 15:08:08,343 setting keymap: rules=evdev, model=pc105, layout=us
15:08:08 ▶ INFO 0a4 [firefox] (xpra-client-stderr) 2018-03-21 15:08:08,399 enabled fast mmap transfers using 256MB shared memory area
15:08:08 ▶ INFO 0a5 [firefox] (xpra-client-stderr) 2018-03-21 15:08:08,400 Xpra X11 server version 0.17.6-r14322
15:08:08 ▶ INFO 0a6 [firefox] (xpra-client-stderr) 2018-03-21 15:08:08,402  running on Linux
15:08:08 ▶ DEBU 0a7 [firefox] (xpra-server) 2018-03-21 15:08:08,405 DPI set to 16 x 21 (wanted 96 x 96)
15:08:08 ▶ DEBU 0a8 [firefox] (xpra-server) 2018-03-21 15:08:08,405  you may experience scaling problems, such as huge or small fonts, etc
15:08:08 ▶ DEBU 0a9 [firefox] (xpra-server) 2018-03-21 15:08:08,405  to fix this issue, try the dpi switch, or use a patched Xorg dummy driver
15:08:08 ▶ INFO 0aa [firefox] (xpra-client-stderr) 2018-03-21 15:08:08,409 Attached to :0 (press Control-C to detach)
15:08:08 ▶ INFO 0ab [firefox] (xpra-client-stderr) 
15:08:13 ▶ DEBU 0ac [firefox] (xpra-server) 2018-03-21 15:08:13,194 Error during encoding:
15:08:13 ▶ DEBU 0ad [firefox] (xpra-server) Traceback (most recent call last):
15:08:13 ▶ DEBU 0ae [firefox] (xpra-server)   File "/usr/lib/python2.7/dist-packages/xpra/server/source.py", line 2100, in encode_loop
15:08:13 ▶ DEBU 0af [firefox] (xpra-server)     fn_and_args[0](*fn_and_args[1:])
15:08:13 ▶ DEBU 0b0 [firefox] (xpra-server)   File "/usr/lib/python2.7/dist-packages/xpra/server/window/window_source.py", line 561, in compress_and_send_window_icon
15:08:13 ▶ DEBU 0b1 [firefox] (xpra-server)     assert wrapper.datatype in ("premult_argb32", "png")
15:08:13 ▶ DEBU 0b2 [firefox] (xpra-server) AssertionError
15:08:14 ▶ DEBU 0b3 [firefox] (xpra-server) 2018-03-21 15:08:14,817 Error during encoding:
15:08:14 ▶ DEBU 0b4 [firefox] (xpra-server) Traceback (most recent call last):
15:08:14 ▶ DEBU 0b5 [firefox] (xpra-server)   File "/usr/lib/python2.7/dist-packages/xpra/server/source.py", line 2100, in encode_loop
15:08:14 ▶ DEBU 0b6 [firefox] (xpra-server)     fn_and_args[0](*fn_and_args[1:])
15:08:14 ▶ DEBU 0b7 [firefox] (xpra-server)   File "/usr/lib/python2.7/dist-packages/xpra/server/window/window_source.py", line 561, in compress_and_send_window_icon
15:08:14 ▶ DEBU 0b8 [firefox] (xpra-server)     assert wrapper.datatype in ("premult_argb32", "png")
15:08:14 ▶ DEBU 0b9 [firefox] (xpra-server) AssertionError

Can this also be related to the amount of shared video memory?
Any ideas?