You can pass a PGO flag to the build system [0], but IIRC from when I was there last, Mozilla puts some serious machine hours into PGO cycles for each release a

You can pass a PGO flag to the build system [0], but IIRC from when I was there last, Mozilla puts some serious machine hours into PGO cycles for each release and that isn't easy to replicate as an individual developer. The profiling captures things which are very specific to the actual build being optimized, so inlining that information into the codebase wouldn't be so helpful. Though there are already static optimization hints spread throughout the code (off the top of my head, MOZ_LIKELY/MOZ_UNLIKELY for marking conditionals). [0] https://firefox-source-docs.mozilla.org/build/buildsystem/pgo.html https://firefox-source-docs.mozilla.org/build/buildsystem/pg...