STR: 1. Increase the number of content processes to 8. 2. Browse as usual. 3. Grab a profile. Sometimes capturing the profile hangs, sometimes it runs out of memory and crashes (e.g. https://crash-stats.mozilla.com/report/index/7ee6a0b1-8fda-4304-be75-c42f22170110 ), and it's altogether a bad experience. One problem here is that the parent process collects all subprocess profiles and stuffs them into one big JSON string. An easy remedy would be to extend the nsIProfiler API to report the profiles of each process separately, and then assembling the different profiles in the perf.html UI, as they come in.