MR520337 are the clips that seat the plastic front bar onto the metal brackets.
There are two 10mm (6x20) bolts that retain the bumper to the 1/4 panel from behind the wheel arch. The holes elongate, and make this seem loose.
There are a stack of re-usable plastic rivet pins over and under the bumper. These do help hold the shape but should not be doing the majority share. You can replace these and the bolts with generic replacements.
Hope this is helpful!