Firefox and plugin-container (Chrome_ChildThr): segfault at 0 ip, sp error 6 in plugin-container/libxul.so

[SK]

parent report : https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1656065

from parent:
```
Hello Robie.

Unfortunately, this problem appeared again. Today, I have had Firefox enabled with just two tabs: YouTube and Google Translate. Suddenly, system start to slow down, disk diode was... red all the time, mouse cursor moved slowly etc. After a couple of minutes, I managed to start terminal and used '$ killall firefox' command, which helped -- system started to work faster again, clicking e.g. on a file, opened Mousepad almost immediately, in milliseconds etc.

Log files (such as '/var/log/syslog' or '/var/log/kern.log') contains:

✓ Sep 4 13:46:00 holycross kernel: [10194.439105] Chrome_~dThread[3599]: segfault at 0 ip b03f6b24 sp afaa1040 error 6 in libxul.so[afb73000+570f000]
✓ Sep 4 13:46:00 holycross kernel: [10195.084439] Chrome_~dThread[4040]: segfault at 0 ip b042fb24 sp afada040 error 6 in libxul.so[afbac000+570f000]

As we can see, there is a problem in 'libxul.so'. (See bug title.) Firefox version: 55.0.2 (32-bit), e10s enabled (4. processes; changed from 2. after update), four addons, no Flash. RAM memory checked with memtest64 - no problems.

I will keep an eye on this, because of a couple of months without problem. Maybe it was just an accident?

Thanks, best regards.
```

I can confirm this bug for
> ii firefox 59.0.2+build1-0ubuntu0.16.04.3 amd64 Safe and easy web browser from Mozilla

at Ubuntu16.04.4 LTS.

```
# dmesg
[14428059.786531] Chrome_~dThread[20444]: segfault at 0 ip 00007f4c6ce2ac26 sp 00007f4c6af2eaf0 error 6 in libxul.so[7f4c6bff8000+580f000]
[14428067.756104] Chrome_~dThread[20745]: segfault at 0 ip 00007f1a0892ac26 sp 00007f1a06a2eaf0 error 6 in libxul.so[7f1a07af8000+580f000]
[14428067.756260] Chrome_~dThread[20829]: segfault at 0 ip 00007f5fe362ac26 sp 00007f5fe172eaf0 error 6 in libxul.so[7f5fe27f8000+580f000]
```

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[SA (superaorta)]

Got this recently in kubuntu 18.04.1 ff 63.0.3

tabs crash and just hang and "webcontent" consumes 100% cpu until killed off. Several times a day. Seems random, once killed same content can be view.