I still test on Firefox because it has been my main browser since the Netscape days (pre-Firefox), but for most customers Chrome, Safari (on iOS) and IE 11 make the bulk of our RFPs browser acceptance matrix (in Germany).
According to GA, on our site, FF is the most used browser, followed by Chrome desktop. 3rd is Chrome mobile and then Safari mobile, tablet, desktop. Only after those, it's IE11 and then Edge. Uniting mobile, tablet and desktop still makes FF 3rd with a 6% lead on IE+Edge.
