I experience them in several different devices; On my main device, I have hundreds of chrome tabs and often many workloads running that would be completely corrupt with random bit flips. I'm not discarding the possibility of faulty RAM completely, I just take the measurement of the tweet with a huge grain of salt - after all, I still remember when the FF team constantly denied - for more than half a decade - that the browser had serious memory leak problems, so its not like there isn't a history of pointing out other causes for FF crashes.