User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/46.0.2490.86 Safari/537.36 Steps to reproduce: https://developer.mozilla.org/en-US/docs/Mozilla/JavaScript_code_modules/WebRequest.jsm#Chrome_incompatibilities I am requesting the ability to modify headers in onHeadersReceived. This would allow for similarity to the Chrome WebRequest extension API. Actual results: Can't modify request. Expected results: The ability to modify the request.

https://developer.mozilla.org/en-US/docs/Mozilla/JavaScript_code_modules/WebRequest.jsm#Chrome_incompatibilities is quite out of date: * We do support onBeforeRedirect (bug 1215197, my first patch landed after quite a long time :) ) * We currently support requestId (bug 1163862) * Fixing bug 1163862 also allowed redirecting from onBeforeRequest, while bug 1231512 should take care of onHeadersReceived (we should add WebExtensions-specific tests, though) * Supporting for modifying headers in onHeadersReceived existed, but was broken by bug 1232849 which, on the bright side, has already a patch waiting for review ;) * onErrorOccurred is tracked by bug 1252596, which I'm gonna fix soon So I think this very bug is either a dupe of bug 1232849 or a bug in the documentation of WebRequest.jsm, which is actually a pain to keep in sync because the most "visible" work happens on the WebExtensions surface, even if this module is still its back-end (same happens for tests, which nowadays are written directly against the chrome.webRequest wrapper).