Earlier quoted context omitted.
I use the nightly builds and I definitely do not have that problem with around 750 tabs open on my non-retina MacBook Pro. It does suck down memory though.
Which doesn't change anything since the Macbook Pro has been sold with Retina displays for what, the last 6 years? The fact that Firefox works exclusively on ancient laptops or edge cases doesn't make anything better. All Apple devices today are sold with Retina screens and the Pro Lineup, and therefore most devs has had Retina screens for 6+ years.
I have periodically had firefox problems in performance on all platforms including the new Mac air I bought my wife, her old Mac Pro and various Ubuntu and Windows installations. As a general rule it is because I've kept it open for several days with lots of tabs with media in them running. I mean it's irritating but not an ongoing catastrophe that means I can't use. As I said in some other thread recently I have over the past 10 years I think had two occasions where FF performance was so bad I had to leave the platform for a some time until it was fixed.
I see a lot of people in this thread claiming problems, and I see a lot of people claiming no problems, and some like me in between. So I don't know what the statistical breakdown of performance complaints about FF in comparison to all other issues (and if those complaints are actually likely to be related), but maybe it is not as great as you think it is?