When Web Content process gets into infinite loop and is unresponsive, there is no way of finding out which tab is causing it

[Paul]

One Web Content process started spinning on CPU and leaking around 300 KiB/s of RAM. The tabs that it was responsible for did not re-render when scrolled, and opening a URL in a new tab failed about 1/4 of the time, presumably when that process was allocated the task. The process and its tabs also didn't show up in about:performance or about:memory, so it was not possible to diagnose which tab was causing the issue. Only three Web Content processes and their tabs appeared there.

This bug was filed when the process reached 6.5 GiB resident. Subsequently, I started closing the tabs that the Web Content process was responsible for. During or immediately after doing so, Firefox killed the process, leaving only three Web Content processes running. The browser seems to be running correctly now on the remaining three.

It would be nice to have some way of determining which tab was the culprit. Even better, for Firefox to kill a tab/process that has got into a hopeless loop.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: firefox 59.0.1+build1-0ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-13.14-generic 4.15.10
Uname: Linux 4.15.0-13-generic x86_64
AddonCompatCheckDisabled: False
ApportVersion: 2.20.9-0ubuntu1
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: pmj 1397 F.... pulseaudio
 /dev/snd/controlC0: pmj 1397 F.... pulseaudio
BuildID: 20180316161208
Channel: Unavailable
CurrentDesktop: KDE
Date: Thu Mar 29 12:25:04 2018
Extensions: extensions.sqlite corrupt or missing
ForcedLayersAccel: False
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
IncompatibleExtensions: Unavailable (corrupt or non-existant compatibility.ini or extensions.sqlite)
InstallationDate: Installed on 2018-03-12 (16 days ago)
InstallationMedia: Kubuntu 18.04 LTS "Bionic Beaver" - Alpha amd64 (20180310)
IpRoute:
 default via 192.168.1.1 dev wlp2s0 proto dhcp metric 600
 169.254.0.0/16 dev wlp2s0 scope link metric 1000
 192.168.1.0/24 dev wlp2s0 proto kernel scope link src 192.168.1.4 metric 600
Locales: extensions.sqlite corrupt or missing
MostRecentCrashID: bp-f519c814-4eea-4087-959f-a338a0180202
PrefSources: prefs.js
Profiles: Profile0 (Default) - LastVersion=59.0.1/20180316161208 (In use)
RunningIncompatibleAddons: False
SourcePackage: firefox
SubmittedCrashIDs:
 bp-f519c814-4eea-4087-959f-a338a0180202
 bp-24a9312a-ec9f-4432-bc1a-254ac0171129
Themes: extensions.sqlite corrupt or missing
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 08/25/2015
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: UX303LAB.210
dmi.board.asset.tag: ATN12345678901234567
dmi.board.name: UX303LAB
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: 1.0
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: ASUSTeK COMPUTER INC.
dmi.chassis.version: 1.0
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrUX303LAB.210:bd08/25/2015:svnASUSTeKCOMPUTERINC.:pnUX303LAB:pvr1.0:rvnASUSTeKCOMPUTERINC.:rnUX303LAB:rvr1.0:cvnASUSTeKCOMPUTERINC.:ct10:cvr1.0:
dmi.product.family: UX
dmi.product.name: UX303LAB
dmi.product.version: 1.0
dmi.sys.vendor: ASUSTeK COMPUTER INC.