Yes, firmer is a Scrabble word!

Adjective

1. Marked by firm determination or resolution; not shakable

2. Not soft or yielding to pressure

3. Strong and sure

4. Not subject to revision or change

5. (of especially a person's physical features) not shaking or trembling

6. Not liable to fluctuate or especially to fall

7. Securely established

8. Possessing the tone and resiliency of healthy tissue

9. Securely fixed in place

10. Unwavering in devotion to friend or vow or cause