_Note: click on the images if they get clipped by other content. Cold startups are those where data has to be read in from disk, warm ones are subsequent startups where the OS already has Firefox files in memory. _ I’m really surprised by the amount of warm startups done by Firefox users. Somewhere between 40% to 60% of startups are warm. On Linux you can see that by watching whether pagefaults occur while loading the firefox binary via EARLY_GLUE_STARTUP_HARD_FAULTS histogram.

On Windows we do not have a good metric  for distinguishing cold startups from warm ones. However can look at the distribution of firstpaint histogram and see that faster startups are more common than slower ones. Only a small minority of machines should be able to cold start a browser in <3 seconds.  We have a lot of startups of various degrees of warmness.

I have no explanation on why people restart Firefox so much. We know < 10% of our shutdowns are unclean (most of those appear to be due to OS shutdown not waiting on Firefox, ie us shutting down too slowly) so users aren’t crashing their browser and starting again. They are voluntarily closing the browser and then starting it soon after (ie OS doesn’t get a chance to flush Firefox out of filesystem cache).

These patterns are pretty consistent across all of the Firefox release channels I checked, so I can’t blame warm startups on nightly users getting barraged with upgrade prompts. Can someone come up with a good theory(preferably with some evidence) for this?

Note telemetry only collects data once a day and requires the browser to be open for a few minutes before submitting data, data could be skewed here.