User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:25.0) Gecko/20100101 Firefox/25.0 (Beta/Release) Build ID: 20130712165549 Steps to reproduce: I was debugging a Linux system crash in the last few days. Actual results: During the crash tests I lost prefs.js several times (xfs filesystem journal recovery deleted it). Expected results: It looks like a missing fsync call causes the data loss and nsISafeOutputStream isn't so "safe" at all. prefs.js is a critical file and data safety trumps performance in this case IMO.
Turned out to be a xfs bug.
Thanks for following up!