Hi Debbie, don't panic just yet.

To get more information about this problem, see whether you can find an error code in the page, it would be in ALL_CAPS and usually starts with SEC_ERROR. On some error pages, you need to click and Advanced button to find the error code.

Copy/paste that code into a reply here, and that will give us a better idea of what to suggest next.

PR_END_OF_FILE_ERROR

That's an odd one.

When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site.

(1) Clear Firefox's Cache

See: How to clear the Firefox cache (just cached web content, don't clear all the site data)

If you have a large hard drive, this might take a few minutes.

(2) Remove your Facebook cookies

In that same section of the Setting page, click the "Manage Data" button to find your Facebook cookies and remove those.

Then try the site again in a new tab. Any improvement?