abstract: Dark energy is interpreted as the leftover of mostly canceled vacuum energy due to the spontaneous mirror symmetry breaking (SMSB) at the electroweak phase transition. Based on the newly proposed mirror-matter model (M3), the extended standard model with mirror matter (SM3) is elaborated to provide a consistent foundation for understanding dark energy, dark matter, baryogenesis, and many other puzzles. New insights of Higgs, top quark, and lepton masses are presented under SM3 using staged quark condensation and four-fermion interactions for SMSB. In particular, the nature and mass scales of neutrinos are naturally explained under the new theory. The new cosmology model based on SM3 could potentially resolve the Hubble tension and other cosmic enigmas. The possible underlying principles for SMSB and SM3 of a maximally interacting, supersymmetric, and mirrored world are also discussed.