I want to set proxy in my system firefox from firefox that I use by VPN.
in VPN's firefox in Preferences/Advanced/Network/Settings the checkbox "use system proxy settings" is checked.
where are system proxy settings definded?
On your Firefox browser select 'Edit' and move to 'Preferences' go to 'Advance' and select 'Network'. To the right-hand side 'Connection'(with configure how Firefox connect to the internet) there is 'Settings...', click on it and and check 'Manual Proxy Configuration' and set your proxy manually.
Then,if you meant to see your system connection information do the following:
Right-click on your network icon on your system panel, at the extreme top corner of your screen and move down to 'Connection Information and select it to see your connection information.