Think normal (double) jig, except three accents to the bar instead of two. Thinking of it as a cross between a jig and a waltz might help, although it sounds totally confusing.

Incidentally you won't be the first to be thrown by 9/8 time. Thomas Hardy senior notated Drops of Brandy in a manuscript book in 4/4 time, with accents every third quaver. And although slip jigs weren't unknown as 17th- and 18th-century dance tunes, Cecil Sharp found alternatives every time for his Country Dance Books. My guess is that he had no problem with them himself, but he knew that the Edwardian schoolmistresses who had to play them on the piano might.