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Tracker looks like *really* busy and *especially* concerned w/ /home/kale/Desktop/Old%20Firefox%20Data/5jtoj909.stable-1530548583684/storage/default/https+++www.theatlantic.com/cache/morgue/71/%7B6754e309-adff-4652-9637-5a3221b64b47%7D.final - what seems über-suspicious…
Likewise some firefox sub-processes crash a lot, but unfortunately in some private xul function.
I'd just move that file out of sight and try firefox against cfq ./. bfq or mq-deadline.
You could check iotop before and after to see whether and what sticks out.
Steam might be an unrelated issue, but there's no indication of it in the journal.
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