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 top view of the concrete fire bowl from FIG. 1;
FIG. 3 is an end view of the concrete fire bowl from FIG. 1;
FIG. 4 is a bottom view of the concrete fire bowl from FIG. 1;
FIG. 5 is a side view of the concrete fire bowl of FIG. 1; and,
FIG. 6 is a side perspective view of the concreate fire bowl of FIG. 1.
The broken lines shown in FIGS. 1 and 4 are included for the purpose of illustrating portions of the article that form no part of the claimed design. The broken lines shown in FIG. 6 are included for the purpose of illustrating environmental context and forms no part of the claimed design.