After removing Firefox from Screen Time and Limits, Elementary OS asks for admin password to open Firefox in child account. Once I supply password, it would still not open Firefox.
This also happened with me. The only way I found to resolve this was to reinstall firefox. I could not find a way to reproduce this easily and it only happened once with me.
After removing Firefox from Screen Time and Limits, Elementary OS asks for admin password to open Firefox in child account. Once I supply password, it would still not open Firefox.