I am using Firefox Quantum on a machine with openSUSE Leap 42.3.
My problem is that Firefox uses a stupid amount of RAM. When I use Chromium I am usually on 2 or max 3 GB of RAM (without doing RAM intense jobs). With Firefox the same jobs require a lot of times up to 5+ GB.
For instance I was simply browsing Facebook and after a while my RAM was at 5.3 GB. I closed just the Facebook tab and it dropped immediately to 1.8 GB.
While using Firefox I have to constantly chech my RAM consumption because after a while it maxes but with Chromium I never have to do that. I have tried playing around with hardware acceleration and such but with no improvement.
Also I want to point out that I have the exact same addons in both browsers.