good luck with your firestones. I bought my last Firestone a while back.
I've had two sets burst belts, through the tread, a decade apart. One was at speed (110+), which could have killed me. they're not getting anymore chances from me.
yes, it was a speed rated tire. all my cars have 120+ rated tires. not the trucks, certainly, but the cars do. I routinely drove 125+ in Germany for several years.
all were relatively new.