These are the answers to some of the queries from google that end up here:
ActiveXObject's in Firefox:
Only IE supports ActiveX.
Microsoft XML (MS XML) Parser in Firefox:
The Microsoft XML Parser objects are ActiveX and thus will not work in Firefox. However, two of the mostly used objects are availble. See the next answer.
XMLHTTPRequest in Firefox:
IE and FireFox/Opera/Safari have different implentations of XMLHTTPRequest. IE uses the object in their XML Parser, while Firefox, Opera (8.0) & Safari uses XMLHTTPRequest. It is initialised like this:
var obj = New XMLHTTPRequest()
See this article from Apple for more information.
Download MS XML Parser 5.0:
To my knowledge there is no public download available of MS XML Parser version 5.0. It is only included in the latest version Microsoft Office.
See my XML sniffer code here. Cross browser version coming soon.