Via prefs, set "offline.startup_state" to 1
(Prefs | Mail & News | Offline | "When starting up: Ask me for online status at
Quit and resart.
Note startup selection. Select either mode button.
use about:config (filter for "online")
Click on any of the offline UI elements (like the button on the lower right).
Note that the pref does not change values interactively.
I think I understand this better now.
Necko keeps the offline-online state internally. Only when
"offline.startup_state" = 0 (remember) should this value be maintained.
The problem is that if we start w/ "prompt me" mode, if you change
"offline.startup_state" to 0, the behavior doesn't change, network.online is not
"offline.startup_state" does not exist anymore