User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:56.0) Gecko/20100101 Firefox/56.0 Build ID: 20171003101214 Steps to reproduce: Click on a context menu of an extension from a sidebar or browser-action page. The context menu and the listener is created according to the attachment. Actual results: The following error was logged to the extension debugging console: TypeError: WeakMap key must be an object, got null ext-browser.js:250:5 Expected results: No error should have occured, and the listener function should have logged its arguments to the console.

Might be something you know how to fix zombie?

Yeah, will investigate.

Comment on attachment 8924325 [details] Bug 1409433 - Handle contextmenu clicks in non-tab content https://reviewboard.mozilla.org/r/195562/#review200840

Pushed by tomica@gmail.com: https://hg.mozilla.org/integration/autoland/rev/759c687e02d2 Handle contextmenu clicks in non-tab content r=aswan

Verified as fixed using Build identifier: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:58.0) Gecko/20100101 Firefox/58.0. Please see console logs comparison between FF57 and FF58. Also, please note that if you test on Windows , extensions.webextensions.remote should be set to false since on Linux(where it was reported) this is false by default.