The ornamental design for a foot warmer releasably secured to a bed, as shown and described.
FIG. 1 is a rear elevation view, of the foot warmer releasably secured to a bed, showing my design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a front elevation view thereof; and,
FIG. 4 is a perspective view thereof wherein the foot warmer is in a substantially open position.
The broken lines showing of parts of the drawings is included for the purpose of illustrating use and environment and forms no part of the claimed design.