I tried i3
focus but it's not working for Firefox only.
My i3 config:
exec i3-msg workspace 1 no_focus [class="Firefox"] exec --no-startup-id i3-msg 'workspace 1; exec /usr/bin/google-chrome' exec --no-startup-id i3-msg 'workspace 1; exec /usr/bin/firefox' exec i3-msg "[class=Google-chrome] focus"
google-chrome to be focused on startup.
I found a related one but it's not useful: Prevent Firefox from taking focus when opening link in other application : i3wm