From Benford's Gilbert and Sullivan Lexicon:
This mini-opera by Burnand and Sullivan is often given as a curtain raiser for Savoy operas. Based on John Maddison Morton’s 1847 farce Box and Cox, the musical version was put together by F. C. Burnand and Arthur Sullivan during a three-week period in 1866. That was for a private gathering; but the “triumviretta” was considered such a gem that it was given a public showing at a charitable performance in the Adelphi Theatre on May 11, 1867. A week later Cox and Box was given a second benefit performance, at another theater, and the reviewer for Fun magazine was none other than W. S. Gilbert, who was not to meet Arthur Sullivan face to face for another two or three years. (His astute comment on the music was to the effect that Sullivan’s notes were too good for the words.)
Cox and Box is a frothy bit of foolishness but it has its virtues, being simple to produce and full of sprightly music. Although out of place chronologically here, it seems appropriate as a brief curtain call.
My libretto is that published by Samuel French of London (undated).