A MenuStrip is a collection of ToolMenuStripItems. Each ToolMenuStripItem is also a collection of ToolMenuStripItems. With that said, in your code, all you have to do is add an item to whichever ToolMenuStripItem you want.
Let's pretend you have a MenuStrip with a ToolMenuStripItem called tsmBookmarks, and Button1 for adding the items:
vb.net Code:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Me.tsmBookmarks.DropDownItems.Add("Your bookmark here")
'or
DirectCast(Me.MenuStrip1.Items("tsmBookmarks"), ToolStripMenuItem).DropDownItems.Add("Your bookmark here")
End Sub
What if you want to capture when their clicked? Let's add an event handler to those ToolStripMenuItems that get created:
vb.net Code:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
AddHandler Me.tsmBookmarks.DropDownItems.Add("Your bookmark here").Click, AddressOf tsmBookmarks_ItemClicked
End Sub
Private Sub tsmBookmarks_ItemClicked(ByVal sender As Object, ByVal e As System.EventArgs)
MessageBox.Show("You clicked: " & DirectCast(sender, ToolStripMenuItem).Text)
End Sub
Now since you said it was a Bookmark you could attach in the tag of the ToolStripMenuItem the web address or something, like so:
vb.net Code:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim tsmBookmarks_SubItem As New ToolStripMenuItem With {.Text = "VB Forums", .Tag = "http://www.vbforums.com"}
Me.tsmBookmarks.DropDownItems.Add(tsmBookmarks_SubItem)
AddHandler tsmBookmarks_SubItem.Click, AddressOf tsmBookmarks_ItemClicked
End Sub
Private Sub tsmBookmarks_ItemClicked(ByVal sender As Object, ByVal e As System.EventArgs)
Dim ItemClicked As ToolStripMenuItem = DirectCast(sender, ToolStripMenuItem)
MessageBox.Show("You clicked: " & ItemClicked.Text)
MessageBox.Show("Make web browser navigate to tag here: " & ItemClicked.Tag.ToString())
End Sub