browser.devtools.panels.elements.createSidebarPane('Gem') return undefined

[mantou]

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/devtools.panels/ElementsPanel/createSidebarPane

[Lusito]

This project only adds type definitions to https://github.com/mozilla/webextension-polyfill. If that function returns undefined and should return a promise, you should probably report the bug there. One exception: If you're encountering this in Firefox, the issue should be reported to https://bugzilla.mozilla.org/