  We study the conductance afforded by a normal-metal probe which is directly
contacting the helical edge modes of a quantum spin Hall insulator (QSHI). We
show a $2e^2/h$ conductance peak at zero temperature in QSHI-based
superconductor--ferromagnet hybrids due to the formation of a single Majorana
bound state (MBS). In a corresponding Josephson junction hosting a pair of
MBSs, a $4e^2/h$ conductance peak is found at zero temperature. The conductance
quantization is robust to changes of the relevant system parameters and,
remarkably, remains unaltered with increasing the distance between probe and
MBSs. In the low temperature limit, the conductance peak is robust as the probe
is placed within the localization length of MBSs. Our findings can therefore
provide an effective way to detect the existence of MBSs in QSHI systems.
