Now there's a few things that are worth mentioning: users with bad hardware will be over-represented in this category, their machines will crash far more often than others.
The second thing is that Firefox is exceptionally stable, we've driven down its crash rate by more than >70% in the last few years. But Firefox is also a 30 million-lines-of-code monster. There are bugs in there, but they're less common than hardware failures! 12/17
Plotting these types of crashes against time yields interesting trends: the more machines age the more likely they are to encounter hardware-related failures. You might think that's obvious, and indeed it is, but until now the industry has looked the other way, based on the hand-wavy excuse that hardware failures were less common than bugs. 13/17