(a) Evolution of the box-averaged magnetic-field strength normalized by the initial background magnetic field. (b) Evolution of the rms speed of electrons (in blue), ions (in red), and the magnetic-field fluctuations normalized by the background magnetic field in black. (c) Evolution of the average temperature ratio, T_⊥/T_∥, for electrons (in blue) and ions (in red), with the associated firehose instability thresholds plotted as corresponding dashed lines. The vertical dashed lines indicate the onset of expansion at ﹩{t}_{{\rm{\exp }}}=0.5{\tau }_{{\rm{\exp }}}﹩ and triggering of the electron firehose instability at ﹩{t}_{{\rm{EFI}}}=0.75{\tau }_{{\rm{\exp }}}﹩.