Catalyzes the conversion of (2E,6E)-farnesyl diphosphate (FPP) into (+)-T-muurolol via a 1,10-cyclization, which requires isomerization of FPP to nerolidyl diphosphate (NPP) and then abstraction of the pyrophosphate from intermediate NPP leading to a (E,Z)-germacradienyl (helminthogermacradienyl) cation. (2E,6E)-farnesyl diphosphate + H2O = (+)-T-muurolol + diphosphate Binds 3 Mg(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. The Asp-Asp-Xaa-Xaa-Asp (DDXXD) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.