What did you do? ================ 1. implement addListener 2. remove a header 3. return the list of new headers What happened? ============== NS_ERROR_ILLEGAL_VALUE: Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE) [nsIHttpChannel.setResponseHeader] WebRequest.jsm:386:0 ------------ the error is in the line channel.setResponseHeader(name, "", false); this line clear all headers before set the new ones in the next lines. here, may be the function channel.setResponseHeader do not accept an empty text as the seconde argument or a header do not accept to be set with an empty text What should have happened? ========================== the new header list should be takin, the old one is! Is there anything else we should know? ====================================== this is the list of headers: ----------------------------------- Cache-Control: no-cache, no-store, max-age=0, must-revalidate Connection: keep-alive Content-Encoding: gzip Content-Language: fr Content-Type: text/html;charset=UTF-8 Date: Mon, 02 May 2016 10:24:43 GMT Expires: 0 Pragma: no-cache Server: nginx/1.4.6 (Ubuntu) Transfer-Encoding: chunked X-Content-Type-Options: nosniff X-Frame-Options: DENY X-XSS-Protection: 1; mode=block

I'm moving your issue to Toolkit - WebExtensions component. Activity Streams is an add-on and has nothing to do with your issue.

giorgio - is this expected or unexpected?

As far as I can tell I should have fixed it in Firefox 47 (bug 1232849): we report failures but don't break the loop, so the new list should replace the old anyway, skipping just the invalid headers. khalid, which Firefox version are you testing?

hi Giorgio, I tested it in 45 and 46.0.1,,, the problem is not due to invalid headers, let me show you the code:(WebRequest.jsm:386:0) --------------------------------------------------------------------------------- if (opts.responseHeaders && result.responseHeaders) { // Start by clearing everything. for (let {name} of responseHeaders) { channel.setResponseHeader(name, "", false); //the problem is in this line } for (let {name, value} of result.responseHeaders) { channel.setResponseHeader(name, value, false); } } --------------------------------------------------------------------------------- a similar situation is when would to clear request header: channel.setRequestHeader(name, "", false); and it works, but channel.setResponseHeader(name, "", false); causes error Best regards.

if can reproduce in 47 - reopen