Some of us have recently been working on improving Firefox’s startup performance. I’m focusing on cold startup, which is heavily I/O bound. You can read about it in my chronicles of startup, which contain notes and thoughts, day-to-day travails, and some scripts for analysis that anybody can run to reproduce my results.
Yesterday I filed bug 510309 to combine XPT files for OS X DMG packages. It should shave a couple hundred milliseconds off of OS X cold startup time spent in I/O. Dietrich, Alice, and I are setting up a Talos Ts to measure cold startup, and that will provide more confidence in this number and more accurate and stable numbers in general.
Update: Jesse pointed out that percentages are helpful when talking about performance. I’ve been getting 8 to 9 wall clock seconds pretty consistently on OS X (simulated) cold startup. Taking the 200ms decrease in I/O (not wall clock time), which is toward the low end of some of the runs I’ve done, that’s a 2.5% improvement over 8s. In the bug linked above I note a decrease of 285ms, a 3.6% improvement. One big caveat is that I was unable to see a corresponding drop in wall clock time in my testing, which is one reason I’d like to get a Talos cold Ts set up.