One example I often run into: Plaid (the bank-linking company) doesn't work. Just hangs. Though I'll admit it's possible they fixed it. I've been trained to use Chrome when I have to interact with it.

I have the same problem. I certainly don't use Chrome daily, but do have to keep it around, typically for shopping checkout and a fair number of US government websites don't work on any browser but Chrome.

jlcpcb's site is often broken in firefox, sadly. i keep chrome around just for it.

Worked for me when I've used it in Firefox. What isn't working?

Try ordering a PCB or seeing the list of house parts for PCBA

Not sure where the list of parts is, but I've ordered PCBs using Firefox.

I used to as well, sometimes it works and sometimes nothing on the page is clickable. New FF profile does not help, chrome works every time and their support has told me many times "we only chrome support sir"

At least they're polite about it. :-)

Some government and hospital websites in Taiwan.

Some startup websites I applied to.

Payment portals are a big one. Non-stripe or PayPal. But even there, if it's a new window payment flow, there can be issues on Firefox.

I've been daily driving Firefox since quantum and up until 2012, but 2fa registration is still needlessly locked out on some sites (need to open up chromium to register the key)

https://business.apple.com simply throws an Unsupported Browser error when trying to visit from Firefox. Unfortunate, but it's another one of those "gotta do it for work" things I deal with.