Use this one instead:
With currBook.Sheets(strNomOnglet)
.Range(.Cells(firstrow, 2), .Cells(firstrow, 8)).Copy _
Destination:=currBook.Sheets(strOngletCibl).Range("B1:H1")
End With
note that I've changed Cells(firstrow, 2)
to .Cells(firstrow, 2)
(to fully qualify your cells, i.e. specify to which sheet they are belongs)
Also if you want to copy only values (without formatting), it's better to use following code:
currBook.Sheets(strOngletCibl).Range("B1:H1").Value = _
currBook.Sheets(strNomOnglet).Cells(firstrow, 2).Resize(, 7).Value
where .Cells(firstrow, 2).Resize(, 7)
is shorter version of .Range(.Cells(firstrow, 2), .Cells(firstrow, 8))