The latest versions of Floatbox (4.11 and 4.12) are making ajax requests twice for "type:ajax" links (according to Firebug). There is a noticeable delay when the box first opens and appears to be loading when the first request is made, then the box resizes to be larger and the request is made a second time.
Example link:
<a href="/terms" class="floatbox" data-fb-options="type:ajax">Terms of Use</a>