File URI Specs
The IE team have written their interpretation of the file:// URI specs. With most operating systems the file: URI is simple, due to the common root used by most non-Microsoft operating systems. For example on Linux /home/dave/index.html would be file:///home/dave/index.html on Mac /Users/dave/index.html would map to file:///Users/dave/index.html but Windows with drive letters and UNC paths had made this more complicated and caused a lot of people using technically invalid URI’s.
One disagreement between Microsoft and Mozilla developers is their interpretation of UNC paths on Windows. These look like \\servername\content\index.html in the blog posting they state:
Incorrect: file:////applib/products/a%2Db/abc%5F9/4148.920a/media/start.swf
Correct: file://applib/products/a-b/abc_9/4148.920a/media/start.swf
However, Mozilla treats the ‘incorrect’ form as the valid form and IE accepts both forms. There’s a reason for this, Mozilla considers all file: URL’s as local even though a UNC path is residing on a different machine it is dealt with by the operating system filesystem layer rather than Mozilla’s network layer.
However, this really doesn’t matter as there’s very little use of file: URI’s for most applications. But it does show how one standard can have different interpretations to different people.