I donate to the Mozilla foundation, and I love Firefox a ton. But I can't seem to like the UI by installing a theme, and when I change it to look better the browser slows to a crawl. Does it really matter all that much if I use Chromium?
P.S. To the people from my last post regarding something similar, Firefox was too slow, I'm sorry, but I use Vivaldi instead of Brave because Brendon Eich can suck my dick.
Browser ram usage will just about always max out the available ram. It's by design. It's keeping open as much as it can for a faster user experience. As you run other programs, the browser should be giving up ram (blanking more tabs) to give it to the programs demanding it.