A half-life of 2.2 $pm$ 0.2 s has been deduced for the ground-state $beta$ decay of $^{84}$Mo, more than 1$sigma$ shorter than the previously adopted value. $^{84}$Mo is an even-even N = Z nucleus lying on the proton dripline, created during explosiv
e hydrogen burning in Type I X-ray bursts in the rapid proton capture ($rp$) process. The effect of the measured half-life on $rp$-process reaction flow is explored. Implications on theoretical treatments of nuclear deformation in $^{84}$Mo are also discussed.
