https://cloudzy.com/blog/which-browsers-use-the-least-memory/
But 64GB is often maxed out for me with multiple installations of FF portable running concurrently, and w/ hundreds of tabs (forums, shopping, etc.).
#26 & 30 I use Firefox all the time with 43 tabs open and right now 4 windows open. I have a Intel Core i5-4690K 4 core CPU @ 3.50GHzand 32gbs of memory and a Gigabyte motherboard from 2015. No issues.
I modified the look and have multi row tabs.
https://davidswebsite.com/Firefox_tabs/firefox_tabs.html