What's your thoughts on Multi-Account Containers? I think it's better to use if your use case for multiple profiles is to keep sessions separate (i.e., keeping work and personal logins to clearly identifiable tabs / windows)
It's not as thorough compared to switching entire profiles but sometimes the above is sufficient. (ex: your history, add-ons and bookmarks are still under the same profile)
I haven't played with MAC (Multi-account Containers) yet but I understand they're a lightweight version of Profiles that can co-exist in a single browser session and have a bunch of neat features (like auto-binding certain sites to certain containers when visited). Would recommend trying out if you've been dissatisfied with the previous approach.
2013 intel chip+integrated graphics runs like a champ and with lower memory usage than chrome (though I am blocking all the ads, which does significantly change performance everywhere).
How about a sane Profile manager? This is something I use heavily on Chrome. The "about:profiles" UI doesn't cut it.
Also when I use Firefox on my non-work Fedora machines (and this is going from Fedora 21 to 29) it seriously chews up memory and CPU. Facebook (yeah, I know) is rendered unusable after about 30 mins. And as other post(s) have pointed out, video playback can be a bit janky. These machines aren't slouches either, i5 ~2.5Ghz 4th or 5th gen, 8GB RAM, SSD, and dedicated graphics cards.
I'd love to switch, but these are things that are deal breakers.