Since a person cannot look at 1000 tabs at the same time, most of the tabs can be frozen. I'm writing to you from Firefox which has 826 tabs right now.

Any browser can use massive amounts of RAM if you open a lot of tabs. Especially if they are running a lot of JS that doesn't release its memory properly. There are some sites I can go to that just continue to chew away at the RAM as long as the tab is open.

In any case, it's pretty easy for the OS to swap out browser data as it is chunkable by tab. Just because it had allocated 22GB doesn't mean that it was all active. Must was certainly swapped to SSD.