IPA: /ˈfɜːr.mli/
KK: /ˈfɜrmli/
In a strong or secure way that shows determination or certainty.
She held the rope firmly to prevent it from slipping.
Firmly → It is formed from "firm" (from Latin "firmus", meaning strong or stable) and the suffix "-ly" (meaning in a manner of). The word "firmly" means in a strong or stable manner.
Think of being 'strong' ('firm') and doing something 'in that manner' ('-ly'). This helps you remember that 'firmly' means doing something in a strong or stable way.