The design consists of the features of shape and configuration, of the FIRE RATED DOWNLIGHT HOUSING as shown in the attached drawings wherein: The design consists of 7 variants comprising FIGS. 7 through 12, FIGS. 13 through 18, FIGS.19 through 24, FIGS. 25 through 30, FIGS. 31 through 36, FIGS. 37 through 42, and FIGS. 43 through 48.FIG. 1 is a top plan view of a fire rated downlight housing in accordance with the design;FIG. 2 is a bottom plan view of the design shown in FIG. 1;FIG. 3 is a perspective view from the top of the design shown in FIG. 1;FIG. 4 is a perspective view from the bottom of the design shown in FIG. 1;FIG. 5 is an end view of the design shown in FIG. 1, the other end being a mirror image thereof;FIG. 6 is a side elevational view of the design shown in FIG. 1;FIG. 7 is a top plan view of a first variant of the design shown in FIG. 1;FIG. 8 is a bottom plan view of the design shown in FIG. 7;FIG. 9 is a perspective view from the top of the design shown in FIG. 7;FIG. 10 is a perspective view from the bottom of the design shown in FIG. 7;FIG. 11 is an end view of the design shown in FIG. 7, the other end being a mirror image thereof;FIG. 12 is a side elevational view of the design shown in FIG. 7;FIG. 13 is a top plan view of a second variant of the design shown in FIG. 1;FIG. 14 is a bottom plan view of the design shown in FIG.13;FIG. 15 is a perspective view from the top of the design shown in FIG. 13;FIG. 16 is a perspective view from the bottom of the design shown in the FIG. 13;FIG. 17 is an end view of the design shown in FIG.13, the other end being a mirror image thereof;FIG. 18 is a side elevational view of the design shown in FIG.13;FIG. 19 is a top plan view of a third variant of the design shown in FIG.1;FIG. 20 is a bottom plan view of the design shown in FIG.19;FIG. 21 is a perspective view from the top of the design shown in FIG.19;FIG. 22 is a perspective view from the bottom of the design shown in FIG.19;FIG. 23 is an end view of the design shown in FIG.19, the other end being a mirror image thereof;FIG. 24 is a side elevational view of the design shown in FIG.19;FIG. 25 is a top plan view of a fourth variant of the design shown in FIG.1;FIG. 26 is a bottom plan view of the design shown in FIG. 25;FIG. 27 is a perspective view from the top of the design shown in FIG. 25;FIG. 28 is a perspective view from the bottom of the design shown in FIG. 25;FIG. 29 is an end view of the design shown in FIG. 25, the other end being a mirror image thereof;FIG. 30 is a side elevational view of the design shown in FIG. 25;FIG. 31 is a top plan view of a fifth variant of the design shown in FIG. 1;FIG. 32 is a bottom plan view of the design shown in FIG. 31;FIG. 33 is a perspective view from the top of the design shown in FIG. 31;FIG. 34 is a perspective view from the bottom of the design shown in FIG. 31;FIG. 35 is an end view of the design shown in FIG. 31, the other end being a mirror image thereof;FIG. 36 is a side elevational view of the design shown in FIG. 31;FIG. 37 is a top plan view of a sixth variant of the design shown in FIG. 1;FIG. 38 is a bottom plan view of the design shown in FIG. 37;FIG. 39 is a perspective view from the top of the design shown in FIG. 37;FIG. 40 is a perspective view from the bottom of the design shown in FIG. 37;FIG. 41 is an end view of the design shown in FIG. 37, the other end being a mirror image thereof;FIG. 42 is a side elevational view of the design shown in FIG. 37;FIG. 43 is top plan view of a seventh variant of the design shown in FIG. 1;FIG. 44 is a bottom plan view of the design shown in FIG. 43;FIG. 45 is a perspective view from the top of the design shown in FIG. 43;FIG. 46 is a perspective view from the bottom of the design shown in FIG. 43;FIG. 47 is an end view of the design shown in FIG. 43, the other end being a mirror image thereof; andFIG. 48 is a side elevational view of the design shown in FIG. 43.The hanging brackets shown at the ends of the housing are shown for position only, and form no part of the claimed design.