Kill the browser twice in a row. You can do it one go by changing browser.sessionstore.max_resumed_crashes to 0 in about:config.

WARNING from the moderator team: Changing Firefox preferences from the about:config page can sometimes break Firefox or cause strange behavior. You should only do this if you know what you're doing. Please read Firefox Advanced Customization and Configuration Options to learn more.

nope. set browser.sessionstore.max_resumed_crashes to 0 and after each of 3 consecutive kills it still starts right up with no session restore tab deselection page. nightly 124.0a1 2024-01-29 64-bit

It works for me with Nightly 124.0a1 (2024-01-30). Make sure you are sending SIG_KILL to the parent process.

Does it still happen in a new profile? Alternatively you can refresh your existing profile. Make sure you stay signed out of your sync account when testing.