How to open an incognito or private window in Chrome or Firefox browsers

Chrome:
Incognito on Chrome (Mac and PC)

Open Google Chrome.
Select the three dot icon in the upper-right corner.
Select New Incognito window from the drop-down menu.
A new window opens, usually darker colored than normal, showing Incognito at the top right.

Firefox:
Private mode on Firefox (Mac and PC)

Open Firefox.
Select the three lines in the upper-right corner.
Select New private Window from the drop-down menu.
A purple-themed window opens, showing a mask at the top right.