Open a direct file on the hard drive from firefox (file:///)

Although i still think it is a programming question, it was answered here: https://superuser.com/questions/103026/open-a-direct-file-on-the-hard-drive-from-firefox-file

Both Firefox and IE8 support the File URI scheme.

Here are some examples valid for Windows systems, referring to the same file c:\WINDOWS\clock.avi

file://localhost/c|/WINDOWS/clock.avi
file:///c|/WINDOWS/clock.avi
file://localhost/c:/WINDOWS/clock.avi
file:///c:/WINDOWS/clock.avi

While the last is the most obvious and human-readable, the first one is the most complete and correct one.

Apparently (from the same url):

Mozilla browsers refuse to follow file URLs on a page that it has fetched with the HTTP protocol.

but:

Mozilla browsers can be configured to override this security restriction as detailed in Mozillazine's "Links to Local Pages Don't Work".

Access to local files in Firefox can't be done unfortunately due to security restrictions. As far as I know (I have asked here repeated times myself) it's not even possible to allow select sites through a configuration setting or similar.

There is a workaround (ponentially unsafe and to be handled with care), you could register a custom protocol as outlined in this question.

Which syntax did you use? The correct syntax for e.g. c:/path/to/file.ext would have been file:///c:/path/to/file.ext. Edit: not relevant anymore as OP has edited his question to include the syntax.

Note that this doesn't work at all if the file is stored at the server machine which in turn is a physically different machine than the client machine (where the webbrowser runs).