It was up against films like Back to the Future, Mad Max Beyond Thunderdome, and Pee-wee's Big Adventure.
I think
Back to the Future was the most popular of the three. It had a much broader audience due to its PG rating and Steven Spielberg's films were known for being box office smashes. And in my opinion,
Back to the Future was far better than
Follow That Bird (I never saw the film due to having outgrown
Sesame Street earlier that year).
Back to the Future was what may have weakened popularity of
The Goonies in the box office, though I believe I may have saw
The Goonies in July 1985.
I also found out just now that Big Bird appeared on NBC's
Today show and on CBC News in Canada to promote the film in the summer of 1985 (That CBC newscast,
Midday, was aired immediately after
Canadian Sesame Street on a daily basis in the mid-1980s). He was even asked on CBC if Snuffy would ever be revealed, and he responded along the lines of "maybe someday." And look at what happened four months later.
I was also amazed that the movie was set mostly in Canada, so maybe this film could qualify as Canadian content. Not to mention that John Candy, one of the comedians who appeared in the film, was also from Canada.
PBS Kids IPs have been notorious bombs at the box office, likely for that reason (see: Thomas and the Magic Railroad & Barney's Great Adventure).
So does that mean
Elmo in Grouchland also bombed at the box office?