I had this problem with playing Netflix videos in Firefox on Fedora where even at video preview-s I would constantly get yellow bar with the message that Widevine Content Decryption Module, required for playing DRM content Netflix serves, has in fact crashed. Videos worked fine in Chrome, but I’d like to use Firefox.

After some digging through, mainly by following Journal logs and triggering error in parallel I’ve came across following error

Nov 18 19:56:01 kirk.tomica.lan systemd-coredump[3869228]: Process 3869223 (MainThread) of user 1000 dumped core.
Stack trace of thread 3869223:
#0  0x00007f69230d54c8 _ZN7mozilla3gmp8GMPChild15ProcessingErrorENS_3ipc14HasResultCodes6ResultEPKc (libxul.so)
#1  0x00007f6923bf83f7 _ZN7mozilla3ipc9IPCResult4FailENS_7NotNullIPNS0_9IProtocolEEEPKcS7_ (libxul.so)
#2  0x00007f6923b89415 _ZN7mozilla3gmp9PGMPChild14OnCallReceivedERKN3IPC7MessageERPS3_ (libxul.so)
#3  0x00007f6923bfa710 _ZN7mozilla3ipc14MessageChannel24DispatchInterruptMessageEPNS0_19ActorLifecycleProxyEON3IPC7MessageEm (libxul.so)
#4  0x00007f6921d88a4b _ZN7mozilla3ipc14MessageChannel15DispatchMessageEON3IPC7MessageE.cold (libxul.so)
#5  0x00007f6924188d11 _ZN7mozilla3ipc14MessageChannel11MessageTask3RunEv (libxul.so)
#6  0x00007f692421f448 _ZN4base18MessagePumpDefault3RunEPNS_11MessagePump8DelegateE (libxul.so)
#7  0x00007f6923defa85 _ZN11MessageLoop3RunEv (libxul.so)
#8  0x00007f6923ddd03b _Z20XRE_InitChildProcessiPPcPK12XREChildData.constprop.0 (libxul.so)
#9  0x000055972ef318ac main (plugin-container)
#10 0x00007f6920f4f1a3 __libc_start_main (libc.so.6)
#11 0x000055972ef1d01e _start (plugin-container)
Stack trace of thread 3869226:
#0  0x00007f692102415d syscall (libc.so.6)
#1  0x00007f6923df1f5e epoll_wait (libxul.so)
#2  0x00007f6923defe89 _ZN4base19MessagePumpLibevent3RunEPNS_11MessagePump8DelegateE (libxul.so)
#3  0x00007f6923defa85 _ZN11MessageLoop3RunEv (libxul.so)
#4  0x00007f6923dea89e _ZN4base6Thread10ThreadMainEv (libxul.so)
#5  0x00007f6923dea79b _ZL10ThreadFuncPv (libxul.so)
#6  0x00007f692758d4e2 start_thread (libpthread.so.0)
#7  0x00007f6921029643 __clone (libc.so.6)

So I was all puzzled on what was triggering this error, and then I’ve noticed, few lines above:

audit[3869246]: ANOM_ABEND auid=1000 uid=1000 gid=1000 ses=1 subj=unconfined_u:unconfined_r:mozilla_plugin_t:s0-s0:c0.c1023 pid=3869246 comm="MainThread"...

Of course it is SELinux! But why? Apparently during the move of my ~/.mozilla folder it had the wrong labels, it was unconfined unlabeled_t, and since the plugin is located in that folder, due to the wrong label, it was crashing as SELinux was killing it (doing its job well).

To resolve the issue I just had to restore labels with:

restorecon -R ~/.mozilla

And it all started working fine after that