  The electron firehose instabilities are among the most studied kinetic
instabilities, especially in the context of space plasmas, whose dynamics is
mainly controlled by collisionless wave-particle interactions. This paper
undertakes a comparative analysis of the aperiodic electron firehose
instabilities excited either by the anisotropic temperature or by the electron
counter-beaming populations. Two symmetric counter-beams provide an effective
kinetic anisotropy similar to the temperature anisotropy of a single
(non-drifting) population, with temperature along the magnetic field direction
larger than that in perpendicular direction. Therefore, the counter-beaming
plasma is susceptible to firehose-like instabilities (FIs), parallel and
oblique branches. Here we focus on the oblique beaming FI, which is also
aperiodic when the free energy is provided by symmetric counter-beams. Our
results show that, for relative small drifts or beaming speeds ($U$), not
exceeding the thermal speed ($\alpha$), the aperiodic FIs exist in the same
interval of wave-numbers and the same range of oblique angles (with respect to
the magnetic field direction), but the growth rates of counter-beaming FI
(CBFI) are always higher than those of temperature anisotropy FI (TAFI). For
$U/\alpha > 1$, however, another electrostatic two-stream instability (ETSI) is
also predicted, which may have growth rates higher than those of CBFI, and may
dominate in that case the dynamics.
