We were asked to determine if EARLY_GLUESTARTUP_READ_OPS affected the startup time for Firefox. It is expected that when the former is 0, the startup time is shorter.
The bug https://bugzilla.mozilla.org/show_bug.cgi?id=757215 describes this in more detail (and a place for the reader to comment).
For our analysis on this, see http://people.mozilla.org/~sguha/757215.html .