Italy or possibly Austria making a play for Libya (although I'm not sure Italy would be ready in the 1860s or 70s).
And yeah, the UK won't be a happy camper - I'd guess that it would at least try to strengthen its position in Egypt, and I wonder if it might not try to take Iraq and/or go for Libya or Tunisia itself as a check against French expansion.
Italy wouldn't be ready in 1875-1878 to make a millitary play for Libya- but OTL 1878 is when they made a diplomatic future claim for it which was largely recognized by France and Austria. If total Ottoman collapse ensues in 1875, rather than Bismark's managed decline in 1878, France might nab Tripoli as well as Tunis, and the U.K would back Egypt in Cyrnecia- and maybe shore it up against further French expansion (loan restructuring?)