Does that annoy you a lot ???

!! To disable autostarting firefox with this readme edit ~/.config/i3/config and comment out this line:

#exec --no-startup-id firefox https://github.com/endeavouros-team/endeavouros-i3wm-setup/blob/main/README.md

~/.config/i3/config is the main configuration file for i3, get into this file and configure i3 as you ike, all settings have comments to give you information about the following setting.