• firstone,
• fireston,
• fiedstone,
• grestone,
• prestone,
• direstone,
• cirestone,
• firestome,
• fierestone,
• friestone,
• fierstone,
• firestonee,
• fyrestone,
• meerstone,
• mereestone,
• ierestone,
• iresstone,
• irestonee,
• pipestonee,
• kiestone

• forester,
• freestone,
• first name,
• firstborn,
• first step,
• fire station,
• first-year,
• forested,
• firstly,
• first off,
• fireside,
• first team,
• firestorm,
• first gear,
• firestine,
• First Reich.

The adjective form of "Firestone" would simply be "Firestone".

The plural of the "firestone" can be the "firestones".

The singular of the "firestone" can be the "firestone".