I was changing a HTML file index.html to be a PHP file called index.php and I renamed my index.html file index.html.bak. The plan was that Apache would find index.php rather than index.html and serve that as the default page. But when I went to load my page Firefox was asking me if I wanted to save the file with MIME type application/x-trash — not what I was expecting! It turns out the problem was related to the index.html.bak file, apparently Apache had decided that was the default page and then when it tried to get the MIME type for .bak it came up with application/x-trash. So the solution was to move the index.html.bak file to something with a filename that didn’t begin with ‘index.html’ (I used ‘original-index.html’) and then once that file had been renamed the index.php page was served properly.