'XMLHttpRequest Level 2' is only partially supported by firefox.

Is this only happening in the Firefox Nightly build or also in Firefox release versions including Firefox 18 beta (Firefox 18 will be released later this week)?

• https://developer.mozilla.org/en/DOM/XMLHttpRequest
• https://developer.mozilla.org/en/DOM/XMLHttpRequest/Using_XMLHttpRequest

Create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

This is also happening in Firefox 17. I have already tried a clean re installation of both Firefox 17 and Firefox 20 nightly. But it didn't solve the problem. I have accidently deleted some windows files in my user folder before. Can that be the one causing this problem?

Did you try a new profile?

A good place to ask advice about web development is at the MozillaZine "Web Development/Standards Evangelism" forum.

• http://forums.mozillazine.org/viewforum.php?f=25

The helpers at that forum are more knowledgeable about web development issues.
You need to register at the MozillaZine forum site in order to post at that forum.

Yes, i tried with a new profile. But it didn't work.