The ornamental design for a concrete firebowl, as shown and described.
FIG. 1 is a top perspective view of the concrete fire bowl embodied in the present invention;
FIG. 2 is a bottom perspective view of the concrete fire bowl from FIG. 1;
FIG. 3 is a front view of the concrete fire bowl from FIG. 1;
FIG. 4 is a back view of the concrete fire bowl from FIG. 1;
FIG. 5 is a right side view of the concrete fire bowl from FIG. 1;
FIG. 6 is a left side view of the concrete fire bowl of FIG. 1;
FIG. 7 is a top view of the concrete fire bowl of FIG. 1; and,
FIG. 8 is a bottom view of the concrete fire bowl of FIG. 1.
The dash-dash-dash broken line shown in FIGS. 3 through 6 is included for the purpose of illustrating environmental context and forms no part of the claimed design.