[williamscales]

In my recollection, Firefox used to ask you which profile you wanted to use on launch. I don't think I've seen that in years.

[precompute]

IIRC you can use the -p flag to open that menu on launch. It also opens when you haven't set a default profile. And it's possible to access other profiles via about:profiles.

[birn559]

You can decide if you want to get asked at startup.