According to Firefox, it uses 25MB. I suspect neither measurement is entirely accurate.

Eight Megabytes and Constantly Swapping.

This too, shall pass. The minimum amount of memory for a double buffered fullscreen surface at 8bpc on a 4k monitor is 48MB. RAM is meant to be used, and if it was not for memory hogs, the DRAM industry would be a decade behind where it is today.