A short bash program to start firefox, capture a profile, and load the resulting profile with samply.

get_profile.sh

#!/bin/bash
set -e

# Start firefox with the profiler running, and capture a profile.
# This is a utility script to quickly run firefox and gather a profile while
# iterating on the format of markers, or other front-end formatting that
# relies on backend changes.

# The time to run the profile. Default to 10 seconds
profiletime=${1:-10}
# The time to gather the profile. Default is $profiletime
gathertime=${2:-$profiletime}

get_profile() {
	# figure out what path `./mach run` will use
	command=$(timeout -s TERM 3 ./mach run | head -n 1 | grep -o "\/.*")
	echo -e "\033[37;45;1;4mRunning: $command\033[0m"
	# Run `command`, and get the PID. 
	# We do it this way (rather than using `mach` directly) as otherwise $!
	# will only tell us the PID of the `mach` program or python
	# We could alternatively use `timeout` again to send SIGUSR2 and SIGKILL
	# but that would prevent us from learning the firefox PID, which we need
	# in order to load the profile using samply
	MOZ_PROFILER_STARTUP=1 $command &
	firefox_pid=$!
	echo -e "\033[37;45;1;4mFound firefox pid: $!\033[0m"
	echo -e "\033[37;45;1;4mSleeping for $1\033[0m"
	sleep $1
	echo -e "\033[37;45;1;4mStarting profile gathering\033[0m"
	kill -s USR2 $firefox_pid
	echo -e "\033[37;45;1;4mSleeping for $2\033[0m"
	sleep $2
	kill -s TERM $firefox_pid
	echo -e "\033[37;45;1;4mLoading in samply: ~/Downloads/profile_0_$firefox_pid.json\033[0m"
	samply load ~/Downloads/profile_0_$firefox_pid.json
}

get_profile $profiletime $gathertime