This is based on data collected by the federal governments Digital Analytics Program (DAP), which analyzes data collected from about 5,000 government websites. In second place is Safari, which is surprising until you read that DAP doesn’t distinguish between desktop and mobile browsers.
I feel sad that Firefox isn’t getting the love it used to receive. When 1.0 was released in November of 2004 I bought a manual, t-shirt, and poster from Mozilla to commemorate the occasion. I still wear the t-shirt.