If you had 80GB worth of websites that did something actually useful with it, you'd want Firefox to use it all.

I usually have dozens of tabs loaded due to usage and I want Firefox to keep all of them into memory so that I can switch between them quicker.

Though I do also want Firefox to shed load by unloading some of them whe I need memory for something else. There just simply isn't a mechanism in Linux to do that AFAIK; Firefox will happily keep all of its tabs loaded all the way until OOM eventhough it could shed most of them with little impact on user experience. There isn't a way for the kernel to ask applications to shed memory load on their own and I think there should be.
macOS has such a mechanism and Firefox uses it but it didn't have much effect IME, so it might have been bugged. That was a good while ago that I tested it though.

Edit: I just found out that there actually is a sort of standard mechanism now: https://systemd.io/MEMORY_PRESSURE/
I don't think firefox implements it but it's also kinda new.