Filed by: ncsoregi [at] mozilla.com
Parsed log: https://treeherder.mozilla.org/logviewer.html#?job_id=312266907&repo=autoland
Full log: https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/bKKuQIzBQPmqv4GmFLfUWw/runs/0/artifacts/public/logs/live_backing.log
Reftest URL: https://hg.mozilla.org/mozilla-central/raw-file/tip/layout/tools/reftest/reftest-analyzer.xhtml#logurl=https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/bKKuQIzBQPmqv4GmFLfUWw/runs/0/artifacts/public/logs/live_backing.log&only_show_unexpected=1

[task 2020-08-06T13:52:35.187Z] 13:52:35 INFO - Assertion failure: mInProcess, at /builds/worker/checkouts/gecko/docshell/base/WindowContext.cpp:321
[task 2020-08-06T13:52:35.187Z] 13:52:35 INFO - #01: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x7c97ae2]
[task 2020-08-06T13:52:35.188Z] 13:52:35 INFO - #02: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x7c98190]
[task 2020-08-06T13:52:35.188Z] 13:52:35 INFO - #03: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x7c96759]
[task 2020-08-06T13:52:35.190Z] 13:52:35 INFO - #04: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x7c9ee67]
[task 2020-08-06T13:52:35.190Z] 13:52:35 INFO - #05: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x7c9e5c4]
[task 2020-08-06T13:52:35.191Z] 13:52:35 INFO - #06: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x7c9ef2c]
[task 2020-08-06T13:52:35.191Z] 13:52:35 INFO - #07: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x4cfe030]
[task 2020-08-06T13:52:35.191Z] 13:52:35 INFO - #08: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x4cfd9b3]
[task 2020-08-06T13:52:35.192Z] 13:52:35 INFO - #09: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x4cfc56e]
[task 2020-08-06T13:52:35.192Z] 13:52:35 INFO - #10: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x4cfd0f2]
[task 2020-08-06T13:52:35.196Z] 13:52:35 INFO - #11: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x4cfd67b]
[task 2020-08-06T13:52:35.199Z] 13:52:35 INFO - #12: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x421ba2a]
[task 2020-08-06T13:52:35.199Z] 13:52:35 INFO - #13: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x421ca09]
[task 2020-08-06T13:52:35.201Z] 13:52:35 INFO - #14: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x4512d0b]
[task 2020-08-06T13:52:35.205Z] 13:52:35 INFO - #15: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x4517a00]
[task 2020-08-06T13:52:35.206Z] 13:52:35 INFO - #16: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x453c35c]
[task 2020-08-06T13:52:35.207Z] 13:52:35 INFO - #17: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x462773e]
[task 2020-08-06T13:52:35.207Z] 13:52:35 INFO - #18: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x463f693]
[task 2020-08-06T13:52:35.208Z] 13:52:35 INFO - #19: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x40e23ab]
[task 2020-08-06T13:52:35.211Z] 13:52:35 INFO - #20: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x40e0d31]
[task 2020-08-06T13:52:35.212Z] 13:52:35 INFO - #21: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x40e017d]
[task 2020-08-06T13:52:35.212Z] 13:52:35 INFO - #22: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x40e02f5]
[task 2020-08-06T13:52:35.213Z] 13:52:35 INFO - #23: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x40e75e9]
[task 2020-08-06T13:52:35.214Z] 13:52:35 INFO - #24: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x40f4be5]
[task 2020-08-06T13:52:35.215Z] 13:52:35 INFO - #25: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x40f8b17]
[task 2020-08-06T13:52:35.216Z] 13:52:35 INFO - #26: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x4728d9c]
[task 2020-08-06T13:52:35.216Z] 13:52:35 INFO - #27: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x46d6a01]
[task 2020-08-06T13:52:35.220Z] 13:52:35 INFO - #28: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x46d695b]
[task 2020-08-06T13:52:35.220Z] 13:52:35 INFO - #29: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x6ee08e7]
[task 2020-08-06T13:52:35.222Z] 13:52:35 INFO - #30: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x8074418]
[task 2020-08-06T13:52:35.222Z] 13:52:35 INFO - #31: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x4729345]
[task 2020-08-06T13:52:35.223Z] 13:52:35 INFO - #32: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x46d6a01]
[task 2020-08-06T13:52:35.224Z] 13:52:35 INFO - #33: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x46d695b]
[task 2020-08-06T13:52:35.225Z] 13:52:35 INFO - #34: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x8073fca]
[task 2020-08-06T13:52:35.227Z] 13:52:35 INFO - #35: content_process_main(mozilla::Bootstrap*, int, char**) [ipc/contentproc/plugin-container.cpp:57]
[task 2020-08-06T13:52:35.228Z] 13:52:35 INFO - #36: main [browser/app/nsBrowserApp.cpp:303]
[task 2020-08-06T13:52:35.237Z] 13:52:35 INFO - #37: __libc_start_main [/lib/x86_64-linux-gnu/libc.so.6 + 0x21b97]
[task 2020-08-06T13:52:35.241Z] 13:52:35 INFO - #38: ??? [/builds/worker/workspace/build/application/firefox/firefox-bin + 0x40029]
[task 2020-08-06T13:52:35.242Z] 13:52:35 INFO - #39: ??? (???:???)

Backed out: https://bugzilla.mozilla.org/show_bug.cgi?id=1611961#c13