Depending on how many distinct actions you've done in the footnote, the
GoBack shortcut Shift+F5 may get you back to the document (it tracks the
last three edits).

Double-clicking the footnote symbol (number, asterisk, whatever) at the
start of the footnote will always take you to the matching symbol in the
text, and vice versa.

Hi,

You can also use a macro, and have the same macro insert the footnote, and return to the text -- see below.
That way, you can use the same keyboard shortcut for both.

The InsertFootnoteNow command (Alt+Ctrl+F) used to work like this in older versions (before Word2000?).

Greetings,
Klaus

If Selection.StoryType = wdFootnotesStory Then
   ' return to main text:
   With ActiveWindow
       Select Case .ActivePane.View.Type
           Case wdPrintView, wdReadingView, _
               wdWebView, wdPrintPreview
               .View.SeekView = wdSeekMainDocument
           Case Else
               .ActivePane.Close
       End Select
   End With
   If Selection.Characters.Last.Style = _
       ActiveDocument.Styles(wdStyleFootnoteReference) Then
       Selection.Move Unit:=wdCharacter, Count:=1
   End If
Else
   ' insert footnote:
   Selection.Footnotes.Add Range:=Selection.Range
End If