The nsMsgNavigationType interface contains constants used for message navigation in Thunderbird. For example to move forward a message, you would call:

 // assuming gDBView is a global nsIMsgDBView
 var resultId = new Object();
 var resultIndex = new Object();
 var threadIndex = new Object();
 gDBView.viewNavigate(Components.interfaces.nsMsgNavigationType.nextMessage,
       resultId, resultIndex, threadIndex, true);

The nsMsgNavigationType interface is defined as a global variable in Thunderbird:

 var nsMsgViewCommandType = Components.interfaces.nsMsgViewCommandType;

mailnews/base/public/nsIMsgDBView.idlScriptable
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  Last changed in Gecko 1.9 (Firefox 3)

Constants

Name Value Description
firstMessage 1 Go to the first message in the view.
nextMessage 2 Go to the next message in the view. Will wrap around if the wrap flag is set to true.
previousMessage 3 Go to the previous message in the view. Will wrap around if the wrap flag is set to true.
lastMessage 4 Go to the last message in the view.
toggleThreadKilled 5 Must match nsMsgViewCommandType toggleThreadKilled.
firstUnreadMessage 6 Go to the first unread message in the view.
nextUnreadMessage 7 Go to the next unread message in the view. Will wrap around if the wrap flag is set to true.
previousUnreadMessage 8 Go to the previous unread message in the view. Will wrap around if the wrap flag is set to true.
lastUnreadMessage 9 Go to the last unread message in the view.
nextUnreadThread 10
nextUnreadFolder 11
nextFolder 12
readMore 13
back 15 Go back to the previous visited message
forward 16 Go forward to the previous visited message
firstFlagged 17
nextFlagged 18
previousFlagged 19
firstNew 20
editUndo 21
editRedo 22
toggleSubthreadKilled 23