Setting a Tab Icon (Favicon) for Each Environment

I often have browser sessions open for each of our environments, but while we have different banner colours to differentiate between DV, PY and PD within E1 it can sometimes be difficult to know which environment belongs to which tab in the browser:

I would like to change the icons within the DV and PY environments so that they show as "DV" and "PY" respectively. Presumably this can be achieved by dropping a favicon file somewhere in the instance's HTML server, does anybody know which folder this would need to go in and if anything else is required to make it work?