Greasemonkey environment is missing cloneInto, createObjectIn and exportFunction

[KarlCastle]

Greasemonkey 2.0 added these three functions to the userscript scope in response to https://blog.mozilla.org/addons/2014/04/10/changes-to-unsafewindow-for-the-add-on-sdk/

Greasespot blog on the topic: https://www.greasespot.net/2014/06/greasemonkey-20-release.html

Tampermonkey added the same functions for cross-compatibility around the same time? I can't find the changelog and, due to the different structure internally, these functions aren't required for userscripts in Tampermonkey.

As of Greasemonkey 4.7 all three functions are still in the global namespace and not using them generates Error: Permission denied to access object errors in Firefox 64.

Recommendation from Greasemonkey to continue using cloneInto() and exportFunction() post-GM4: https://www.greasespot.net/2017/09/greasemonkey-4-for-script-authors.html

Documentation from Mozilla, updated in September 2018: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Sharing_objects_with_page_scripts#Sharing_content_script_objects_with_page_scripts

I'll put together a PR.