I get issues almost daily with well respected sites not working in Firefox.
Today I'm browsing the Adidas website, and the images don't load for any of the products in Firefox.
https://www.adidas.com/us/ultraboost-all-terrain-ltd-shoes/B...
Apparently they're WEBP images and my version of Firefox (version 64) doesn't support them, but searching online I read that the upcoming Firefox version 65 is suppose to fix that issue.
Strangely enough, the images were working fine a few weeks ago on the Adidas website, but I had a different Firefox issue. When I clicked the images to see the fullscreen view and zoomed in, they wouldn't pan or drag correctly, so 80% of the image was hidden off the screen. In Chrome, they worked as expected.
That's one example, but as I said, I get these kind of issues almost daily from companies that should know better. I still primarily use Firefox because I have no trust in Google, but I'm forced to open Chrome on a regular basis to resolve random quirks.