Here is a main “check” list for you:

• Check that you don’t have any image or another elements in View with empty src attribute (<img src=”" /> for example) or have src attribute referencing something that no longer existed. You better check directly in browser “Page Source”, than in View itself due to possibility of some “dynamic” issues when View rendered. Ones you found such empty element in page html source its usually trivial to found same element in your view and fix issue.
• Check that you don’t have any ajax calls referencing an empty URL (browsers will interpret such empty url as current page and request current page again make controller action execute few times)
• You forgot to return “false” from JavaScript click event handler for link or button that makes AJAX call. If you forget “return false” browser simply made default action of the link – regular, non AJAX, call to same page)
• Sometimes Firebug and YSlow Firefox (FF) plugins can cause such issues… Just temporary disable them in FF or check in different browser.

Know another reason? Let me know!