I did some investigating, and this seems to be caused by two bugs (that I can tell). One, that Facebook's API causes a bug in IE that sends this query in the first place, and second that my website, because of the Facebook API, causes the page to become visibly blank because of it.
So, what to do? I decided to kill the query string at the source: my apache web server using mod_rewrite.
So here's what I added to the apache config for just this web server:
RewriteEngine On
RewriteCond %{QUERY_STRING} fb_xd_fragment=
RewriteRule (.*) $1? [R=301]So this basically sends a 301 HTTP code (Moved Permanently) with the same request, minus the query string. Note that the "?" on the RewriteRule is needed so that mod_rewrite doesn't append the old query back on. Seems to be doing the trick, and now I'm not losing traffic due to a Facebook API bug.