User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; nl; rv:1.9b5) Gecko/2008032620 Firefox/3.0b5
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 6.0; nl; rv:1.9b5) Gecko/2008032620 Firefox/3.0b5
According to the XMLHttpRequest specification , “[the User Agent] must not
automatically set the Accept [header]”. Currently, Firefox 3b5 sends ‘Accept:
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8’. This is incorrect, and should be fixed to not send an Accept header at all.
The rationale behind the specification is that when an Accept header is not set
explicitly, we do not know what the application expects. Setting a default
Accept header effectively means that we are lying to the server, and breaking
correct functioning of HTTP content negotiation.
For further details and a test see my blog post .
Steps to Reproduce:
1. Go to http://www.grauw.nl/blog/entry/470
2. Try the test by clicking on the button
Server receives Accept header with contents "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"
Server should not receive an Accept header at all.
Note that this bug references the 15 April 2008 working draft of the spec.
Additionally, Firefox needs to line up with other browsers (or other browsers need to line up with Firefox :)) with regard to setRequestHeader('Accept', '') and setRequestHeader('Accept', null).
See also discussion on the W3C WebAPI WG list:
If the user agent implements server-driven content-negotiation it must follow these constraints for the Accept and Accept-Language request headers:
o Both headers must not be modified if they are already set through
o If not set through setRequestHeader() Accept-Language should be set
o If not set through setRequestHeader() Accept must be set with as
is all I can find about 'Accept' in <http://dev.w3.org/2006/webapi/XMLHttpRequest-2/>.
I came across this bug via a random Google search. Setting a dependency. It may or may not already be fixed, but at least, it won't be an orphan any longer.
Seeing this in version 42.0
Wow! It is 2016 and this bug in Firefox 44 still exists. Please fix to conform to the XMLHttpRequest standard.
The requirement is now in https://fetch.spec.whatwg.org/#concept-fetch