Slightly off topic, I'm finding it very disingenuous that people in this thread(and any other threads that come up about Firefox) have actually had significant performance issues with Firefox. No bugs that are noteworthy, sans that fiasco with the expired certificate that disabled addons briefly. I've been using Firefox since "quantum" on both my MacBooks(one of which is old AF) and on Linux. I've yet to have problem…
Quantum improved it, but I still have lots of issues with Firefox on Linux. To name a few: (For reference I'm running Firefox 67 on NixOS, xmonad, no DE, 7700K, 64GB RAM, RTX2070, only extensions I use are uBlock Origin, Panorama View, but I've run into all the problems below in safe mode also)
* Still slower than Chrome if you use lots of tabs and windows (generally 100+ on 3 windows depending on current jobs). It's much faster than it used to be but I can't deny when I have to switch back to Chrome for some things, I'm surprised at the (slight) speed difference.
* Visual glitches with lots of tabs the tab bar will occasionally spasm, sometimes all the text will disappear etc.
* Sometimes a window will just stop working. All the tabs are still there, but they all show blank white pages, new tabs are also blank. Different windows will work and a new window will work. Restarting firefox, the same window will be all blank pages. The only solution I've found is open a new window and copy the tabs you want to save one by one to the new working window.
* Bunch of websites just don't work in Firefox. In particular several of my governments payment portals don't work in Firefox on Linux but work fine in Chrome.
* Sometimes I get crackling audio from Firefox that can only be fixed by restarting pulse, never had it happen in Chrome.
* Some streaming websites choke firefox out, for example ufc.tv PPVs are sometimes entirely unwatchable in FF, the audio and video fall out of sync after a few minutes, sometimes it can makes other tabs sluggish. Never have a problem with Chrome, will usually just open a chrome window to watch live streams.
I chalk most of these up to Linux weirdness, but I do quite often find myself annoyed at FF considering its running on a moderately well specced machine, and its literally the only app I run regularly that gives me heartache.
That being said I've stuck with FF over Chrome and still prefer it for various reasons and recommend people try it. I just disagree with the idea I see floating around that there's nothing wrong with FF at all and its just as fast and stable as Chrome. It's not been my experience.