We have used FF on various devises for many years. It WAS a stable and reliable browser. Recently it has become an almost constant source of irritation and frustration. Apart from other things, like certificate and site loading issues, often, when we reduce the browser and reopen it all except the home tab disappear. And restore session is always greyed. Yes, we have searched for solutions and tried myriad fixes - none work. We have been forced to defile our macs with chrome. Apple are still lost in the jungle on safari.
Sorry, but you have stuffed up a once great browser. .