Is there any way to remove the Delete or Detach options from the attachment right-click menu? I find myself clicking them too often by accident, and am afraid I may end up losing something eventually.
Menu Editor will allow you to customize the contect menus of Firefox and Thunderbird.
This probably isn't good fore FireFox any more since it was released on march 8, 2011. However, Thunderbird almost never releases new updates so it should still work for you there.