Volume 2 — Chapter 19:
Reading edition
On Page 56, fire-ships is hyphenated in the clause: At the end of May Admiral Boscawen was at Halifax with twenty-three ships of the line, eighteen frigates and fire-ships, and a fleet of transports ... Fireships is used eight other times in these volumes without a hyphen. The inconsistency came from the publisher or author, not the transcriber.