We've tested on a number of browsers but not often enough on some of them - like Firefox. We don't like all the data Chrome collects on it's users, but it makes up for the vast majority of usage on desktop and Android so it's important to test it most thoroughly on the most thoroughly used browser. We did the same on Safari which is a bit more private than Chrome, but not totally. We need to test more, perhaps something like browserstack needs to make it's way back into my toolchain.