It's hard to tell exactly, but if you look at the numbers you can see that, for example, Firefox and Safari don't support WebUSB or APIs for accessing things like the accelerometer or ambient light sensor of the device the browser is running on the device the browser is running on (this is by choice I believe) or things like Scalable Video Coding for WebRTC (rtc-svc).
It's hard to tell exactly, but if you look at the numbers you can see that, for example, Firefox and Safari don't support WebUSB or APIs for accessing things like the accelerometer or ambient light sensor of the device the browser is running on the device the browser is running on (this is by choice I believe) or things like Scalable Video Coding for WebRTC (rtc-svc).