IE7 breaks some AJAX libraries

Probably this is very old news (and Internet is full of related blog entries), but somehow I've managed to miss it ... If you use XMLHTTP Request object and initialize it similar to this:

if (IE) {
  x = new ActiveXObject("Microsoft.XMLHTTP")
} else  {
  x = new XMLHttpRequest();
}

... Internet Explorer 7 will constantly complain about the page trying to use ActiveX controls (at least IE6 was silent unless you've disabled ActiveX in which case AJAX broke anyway). The proper way to deal with this particular quirk of IE is to test for window.XMLHttpRequest first (instead of relying on browser type) and use ActiveX only if needed.

Note: If you use Sarissa (which broke my AJAX application), download the latest version, it contains all relevant IE7 fixes.