I have the following code:
...
<head>
<title>Alternative Style Sheet Example for MDC</title>
<link href="./default.css" rel="stylesheet" type="text/css" title="Default Style">
<link href="./simple.css" rel="alternate stylesheet" type="text/css" title="Simple">
<link href="./insane.css" rel="alternate stylesheet" type="text/css" title="Insane">
</head>
...
(from https://developer.mozilla.org/samples/cssref/altstyles/index.html). If I open a local copy of the html file in Firefox, the alternate stylesheets do not show up in Firefox under 'View > Page Style', I can only see 'No Style' and 'Basic Page Style' option. However, if I open the link above, all the stylesheets show up correctly in the selection ('No Style', 'Default Style', 'Simple' and 'Insane'). Also tested in Chrome with Alt CSS extension, same behavior.
How can I make the options visible for the local copy too?