But their faith is firm (7)

I believe the answer is:

quakers

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'firm' is the definition.
The answer and definition can be both groups as well as being singular nouns.
Maybe you can see a link between them that I can't see?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Another definition for quakers that I've seen is " Society of Friends members".)

I've seen this clue in The Globe and Mail.

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