I suspect this could be GNOME Shell, not us.

I just tried the patch with metacity. The application menu is embedded in the window as "Web" and has all the items. This works for private and non private instances.

A quick look at GNOME Shell's code in js/ui/panel.js shows that it is either the model as mined by the Shell or the fallback Quit menu.

Since we are seeing the empty menu, it is trying to use the mined model.
We have to find why it is breaking for our case.

Created attachment 207182 [details] [review]
ephy-shell: set the application menu for private mode

(In reply to comment #2)
> Created an attachment (id=207182) [details] [review]
> ephy-shell: set the application menu for private mode

Reference patch. Apply this and:
- run epiphany -p => empty application menu.
- run epiphany, don't close it, then epiphany -p => application menu on both

I'm suspecting this is because of G_APPLICATION_NON_UNIQUE not being handled correctly by GNOME Shell.

d-feet shows that regular Epiphany registers in DBus with /org/gnome/Epiphany and the org.gtk.Actions interface. Private mode doesn't, because of NON_UNIQUE.

This results in the object path for menu existing, but not the org.gtk.Actions interface needed to fill such menu.

Not sure how to do this. Should ask the people that do know.

I've pushed the obvious fix for this to master. It's still broken because non-unique apps are not in the bus, see bug #647986.