I don't use Gmail anymore as a primary address, but when I do check my old address, Gmail takes up to 30 seconds to load on Firefox. Emails often take several seconds to delete, and if I close the tab a few seconds after deleting the emails, they don't actually get deleted, even if they appear to.

I am not sure what exactly Gmail does on Firefox, but it makes using AOL.com in 2020 feel like a better email experience.

That’s something broken with your Firefox install or computer then. It’s very performant on any of my two G Suite and one Gmail accounts on Firefox as well as Chrome.

Or something broken in how Gmail handles a wide variety of Firefox installs/configurations (this is a common reported issue). The fact that you personally haven't seen it ("works on my machine!") doesn't mean the issue doesn't exist.

Interesting. Are you exaggerating a bit here or being accurate with those timelines? Cos Gmail is really slow on Firefox for me too, but it doesn't take half a minute to load. More like 10-15 seconds, which in this day and age is a nonsensical amount of time. Similarly operations have a 2-3 second lag. Noticeable to normal users but people like my parents wouldn't be able to see it.