Finding your way around epiphany is a big headache. It is based on firefox but nothing is kept like firefox. For example, if you are trying to locate proxy settings inside epiphany, stop it now. That setting is kept outside the browser.

Epiphany accepts proxy settings from GNOME settings. To set proxy in GNOME, go to a terminal and execute the command “gnome-network-preferences“

$ gnome-network-preferences

A window similar to this will pop up. Adapt the settings according to your requirement.

Remember: For every user you will have to set this proxy configuration.