[hyperlink] How link to any local file with markdown syntax?

This is a old question, but to me it still doesn't seem to have a complete answer to the OP's question. The chosen answer about security being the possible issue is actually often not the problem when using the Firefox 'Markdown Viewer' plug-in in my experience. Also, the OP seems to be using MS-Windows, so there is the added issue of specifying different drives.

So, here is a little more complete yet simple answer for the 'Markdown Viewer' plug-in on Windows (and other Markdown renderers I've seen): just enter the local path as you would normally, and if it is an absolute path make sure to start it with a slash. So:

[a relative link](../../some/dir/filename.md)
[Link to file in another dir on same drive](/another/dir/filename.md)
[Link to file in another dir on a different drive](/D:/dir/filename.md)

That last one was probably what the OP was looking for given their example. Note this can also be used to display directories rather than files.

Though late, I hope this helps!