Grease a 6-cup fish mold with butter or mayonnaise. Soften the gelatin in 1/4 cup cold water. Add 1/2 cup boiling water and stir well, until the gelatin has dissolved. Add the mayonnaise, lemon juice, lime juice, onion, hot sauce, paprika, and salt and mix well. Fold in the salmon and capers. Add the whipped cream and contine folding until everything is well combined. Pour the mixture into the prepared mold. Cover with plastic wrap and chill in the refrigerator for 8 hours or overnight.
To make the dill sauce, combine all the ingredients in a medium bowl. Cover with plastic wrap and chill for at least 1 hour.
When ready to serve, unmold the mousse onto a large plate. Take the lemon slices and create a "tail" on the back of the fish. Surround the mousse with parsley. Serve the dill sauce in a glass bowl next to the salmon mousse.