I tried firefox-perf tonight. The libffi7.tcz is missing when installed. I installed it manually. It started but I was kind of locked out of https sites. Either I was told that I was not autorized or the page did not work as supposed. I tried to start firefox-perf from a terminal and there I saw that libffi.so.7 was missing. So it seems that firefox-perf needs some maintenance. Now I am going to try out the firefox-ESR.
Kind Regards,
meo