But none that describe the cause of the bug, right?
So yes?
ctrl+f to find user "fukusa" and you'll find that one of his/her comment goes into depth.
[1] https://github.com/mozilla/gecko-dev/commit/2e67509c8a3cefe8...
[2] https://github.com/mozilla/gecko-dev/commit/8b7f7bde8f21bd71...