Growth rates of the firehose instability as provided by Eq. (14) for κ_e = 2, κ_p = 3 (dotted line), κ_e,p = 4 (dashed line), κ_e,p → ∞ (solid line), and plasma parameters: T_e,∥/T_e,⊥ = T_p,∥/T_p,⊥ = 4, a) T_e,∥/T_p,∥ = 3, β_e,∥ = 18; and b) T_e,∥/T_p,∥ = 2, β_e,∥ = 8. For a given wave-number value K = 0.03, the growth rate variation with κ_e and κ_p is shown in panel c). (W_i = ω_i/Ω_p, K = kc/ω_p,p).