As an Apple user for decades, have to say that High Sierra seemed to be one of their better recent releases.
I have an iMac that uses it and a Mac Mini that is on Mojave and for some reason, High Sierra just feels more stable with some software.
Firefox runs fine on High Sierra and has crashed multiple times in the past few weeks after using it on Mojave.
Maybe I'm just biased having used High Sierra for so long and dreading Catalina lol.