Look up firmus in Wiktionary, the free dictionary.
Firmus (died 273) was a usurper during the reign of Aurelian.
Firmus may also refer to:
- Firmus (4th-century usurper) (died 375)
- Firmus and Rusticus, 3rd century saints
- Firmus Energy, a Northern Ireland energy company
- Admiral Firmus Piett, a fictional character in Star Wars