Since Firefox displays the link correctly when you just type it in or use the Open File dialog, this may not be the problem, but the issue may be Java permissions related to the browser. If the URL is indeed the same when you type it in or search for it and when you click a link displayed in XWiki, this may not be the case (and of course it won't be if Firefox doesn't implement that in Java), but if it is, it will likely be because there's a difference in user volition between a deliberate entry of a URL through the address bar or file-open dialog and just clicking a link displayed on a page from another host. To test my hypothesis, I'd suggest creating an HTML page in the same directory as the file that won't load, copying that link into it, and then opening that page and seeing whether the link loads. If it doesn't, it's very likely to be Java permissions granted to the browser; if it does, it may be something in Firefox related to the permissions you grant to that host. I'm not aware specifically of that being one of the permissions that Firefox allows you to grant to hosts, but it does give you control over such things as whether to execute Java or Javascript or allow popups, and other potentially annoying or dangerous things. Likewise, you can probably make IE misbehave the same way if you mess with the settings in its Network Zones, or whatever it is that they call that... brain[sic]