nsISessionStartup
browser/components/sessionstore/nsisessionstartup.idlscriptable handles the session restore process.
... 1.0 66 introduced gecko 1.8 inherits from: nsisupports last changed in gecko 8.0 (firefox 8.0 / thunderbird 8.0 / seamonkey 2.5) implemented by: @mozilla.org/browser/sessionstartup;1.
... to use this service, use: var sessionstartup = components.classes["@mozilla.org/browser/sessionstartup;1"] .getservice(components.interfaces.nsisessionstartup); method overview boolean dorestore(); attributes attribute type description sessiontype unsigned long the type of session being restored; this will be one of the session type constants.

Make your xulrunner app match the system locale - Archive of obsolete content
the code described lives in the pybridge component's onstartup method which gets called automatically.

Index
906 nsisessionstartup interfaces, interfaces:scriptable, xpcom interface reference, sessionstorage implemented by: @mozilla.org/browser/sessionstartup;1.

nsISessionStore
nsisessionstartup json ...

XPCOM Interface Reference
creennsiscreenmanagernsiscripterrornsiscripterror2nsiscriptableionsiscriptableinputstreamnsiscriptableunescapehtmlnsiscriptableunicodeconverternsiscrollablensisearchenginensisearchsubmissionnsisecuritycheckedcomponentnsiseekablestreamnsiselectionnsiselection2nsiselection3nsiselectioncontrollernsiselectionimageservicensiselectionprivatensiserversocketnsiserversocketlistenernsiservicemanagernsisessionstartupnsisessionstorensisimpleenumeratornsismsdatabaseservicensismsrequestmanagernsismsservicensisocketprovidernsisocketproviderservicensisockettransportnsisockettransportservicensisoundnsispeculativeconnectnsistackframensistandardurlnsistreamconverternsistreamlistenernsistringbundlensistringbundleoverridensistringbundleservicensistringenumeratornsistructuredclonecontainernsistylesheetservicensisupports...

MailNews fakeserver
onstartup none server's response called when a connection is made.