I notice the Field of View (FOV) degree per street view zoom level is different between browsers
I believe the documented street view zoom level to FOV is
Currently, there is a table here relating zoom and FOV that says:
0=>180 1=>90 2=>45 3=>22.5 4=>11.5
You can convert from zoom to FOV in javascript like this:
var fov = 180 / Math.pow(2,zoom);