You can't unfortunately specify just the firewall section for read/write access.
You can configure command authorization for specific command that you would like read/write access, however, in your case, the command would be access-list and access-list can belong to different section, ie: firewall, NAT, VPN, etc.
If you are interested, here is the document on command authorization for you reference:
Otherwise, the ASA only have 3 level of privileges:
- Admin (privilege level 15, with full access to all CLI commands;
- Read Only (privilege level 5, with read-only access); and
- Monitor Only (privilege level 3, with access to the Monitoring section only).