Hi CleverPhd and Dmitri,
You are both right, not only Facebook but all other servers are configured to ignore the extra slashes in the URL. This can be a problem for sure for crawlers, as they would treat each URL as different (if asked to index). Moreover, there are infinite number of URL you can produce with this example.
As per URI (http://www.ietf.org/rfc/rfc2396.txt) standard, each slash has a significance. If you test the same phenomenon with Ealier browsers of IE, you will realise that they don't reproduce the same effect, the pages would be missing elements are they fail to find the location of the resources required for the page.
The problem is with the how our servers are configured these days to ignore the extra slash and produce the same page as a result.
There a quick fix on Apache with mod_rewrite code (you can add more lines to cover 3 or more slashes) which would produce 301 redirect to the right page
<code>RewriteCond %{REQUEST_URI} ^(.*)//(.*)$
RewriteRule . %1/%2 [R=301,L]</code>
I hope this helps,
Regards,
Vijay