Missing the reason

My experience - of running 64-bit Firefox on an x64 system with 2-8GB RAM and no swap - is that while it doesn't crash, it does occasionally decide to try and use all of the 28GB it has allocated, which rapidly brings the entire system to a halt as executable pages are crowded out by dirty data pages with nowhere to go. This has been depressingly repeatable across every system I've tried it on, and is why I switched back to using 32-bit Firefox in the first place.

Call me old-fashioned, but I would rather have the browser segfault than DoS the entire system it's running on... which, as I understand it, isn't fantastic for security either, to address another point raised in these comments.