if additional headers are added to a HTTP request, and that request results in a redirect, the newly created request will not have any of the additional request headers added to the original request. in some cases this is undesirable. see news thread here: http://tinyurl.com/kofx

-> default owner

Is this the same as bug 401564?

doing the opposite (copying them blanket) is also undesirable. I think we've made our peace here by copying a particular subset iirc

Note that the XHR code re-adds any custom headers that were set on redirect. I'm fairly sure the web depends on this behavior. fetch() does currently not. I don't have a strong opinion about what to do in general.

Per Fetch everything the API layer adds should be copied. This is based on what XMLHttpRequest already does. If fetch() does not have that behavior it would be a bug.

(Same by the way for EventSource, e.g., Last-Event-ID should not be dropped along the way. Or <a ping> headers.)

This is already fixed in FF46.

Actually, it's fixed in FF45 as well.