This is a regular verb. It follows the conjugation pattern of the verb falar.
The verb firmar can also mean 'to sign' (e.g., firmar um contrato), but this usage is more formal. In everyday language, assinar is more commonly used.
Present:
A Ana firma parcerias fortes.
Ana establishes strong partnerships.
O diretor firma o contrato.
The director signs the contract.
Preterite:
O Miguel firmou o acordo.
Miguel secured the agreement.
Future:
(Ela) firmará uma nova estratégia.
She will establish a new strategy.