We study electron dephasing in a large quantum dot (a Fabry-Perot interferometer) in the fractional
quantum Hall regime with filling factor 2/3. In the regime of electron sequential tunneling
into the dot, dephasing occurs due to electron fractionalization into counterpropagating charge and
neutral edge modes on the dot. In particular, when the charge mode moves much faster than the
neutral mode, and at temperatures higher than the level spacing of the dot, electron fractionalization
combined with fractional braiding statistics of the charge mode leads to the suppression of h/e
Aharonov-Bohm oscillations, resulting in period halving h/(2e) oscillations.