From MozillaZine Knowledge Base
Firefox 3 gained support for offline/online status detection in Linux, using capabilities in NetworkManager. However, if NetworkManager was not controlling the active network interface, Firefox would incorrectly switch to offline mode. This resulted in Firefox starting up in offline mode even when a network connection was available.
To work around the problem, this preference allows users to disable offline status detection via NetworkManager.
Possible values and their effects
Do not use NetworkManager to detect offline/online status.
Use NetworkManager to detect offline/online status, and switch between offline/online modes in Firefox. (Default)
If you use a PPP connection (dialup or DSL) and Firefox always starts in “Offline” mode, switching this preference to true may fix the problem. Offline/online status changes will not be detected, though.
First checked in
2008-06-30 by Reed Loden (patch by Wolfgang Rosenauer)
Has an effect in