Beth,
If you don't plan on using MUMPS anytime soon, then run firedrake-install with --minimal_petsc. If you want to keep all the other options (hdf5, exodusii, etc), then you can add back everything but --download-mumps and --download-scalapack to your PETSC_CONFIGURE_OPTIONS.
Perhaps unrelated or irrelevant, but maybe try using Homebrew's python instead and not Enthought's python? Also run using --developer to ensure that this python version doesn't conflict with whatever other python environments you have set.