The timings that are currently reported through this API are the following:
- process is when the Firefox process starts
- main is when the
XRE_mainfunction is called (one of the first functions actively called)
- firstPaint is when a web page has been displayed for the first time to the user
- sessionRestored is pretty much self describing
There are apparently still a few rough edges, but it is still quite valuable information. As such, I wrote a little (restart-less) extension that displays these information when you go to the about:startup url. It doesn’t really display the raw values, but instead the number of milliseconds elapsed since the process startup until each further event above.
In the long run, we should have a fully fledged extension doing that.