Are on firm ground - Idioms by The Free Dictionary
be on firm ground (redirected from are on firm ground)
be on firm ground
To be certain of or comfortable with something. Anna can tutor you—she's on firm ground with diagramming sentences.
be on firm ground be sure of your facts or secure in your position, especially in a discussion.
be on firm ˈground be sure about your beliefs, knowledge, etc.; be confident: I don’t know a lot about physics, I’m afraid. I’m on firmer ground with mathematics, which I studied at university.