As a security precaution, Firefox forbids sites on the Internet to link to files that are stored in your local computing environment. These files may include files on your computer, mapped network drives, and UNC network paths. However, some sites such as corporate intranets require this access to the local computing environment and may indicate that a link is broken if local access is not permitted.

Diagnosis

To see if this security measure is the source of the problem, you can check the Firefox Error Console:

1. In Firefox, open the page that contains the problem link.
2. At the top of the Firefox windowOn the menu bar, select the Tools menu, and then select Error Console.
3. Click Clear.
4. Click All.
5. On the main Firefox window, click the problem link.
6. Check the Error Console. The security measure is the source of the problem with the link if you see an Error Console entry similar to the following:
   Security Error: Content at (address) may not load or link to (address)

Fix

To fix this problem, provide this article to your system administrator, who should be able to either fix the site or configure your Firefox to work with the site.

Workaround

As a temporary workaround, you can use the LocalLink extension. This extension give you the ability to bypass the security restriction on local files.

1. After installing LocalLink, open the page with the problem link.
2. Right-clickHold down the Ctrl key while you click the link.
3. In the Open menu, choose Open. Firefox should now open the site without a problem. Unfortunately, LocalLink doesn't remember which links you choose to allow, so you'll have to do this every time.

Based on information from Links to local pages do not work (mozillaZine KB)