How to access about:config programmatically

Hello friends: I need to set some config properties in Firefox 51 to let screen sharing / desktop capturing. I have seen that with the add-on philosophy, we could acces to the sdk/preferences/service api. But in the Web Extension philosophy, this way has changed. I need to set the next properties:

media.getusermedia.screensharing.enabled = true.
media.getusermedia.screensharing.allowed_domains = Add my domain to this white list.

I have also seen something about “permissions” key in manifest.json, but I can’t get this working.

I don’t want the user to go to about:config page. I want to set that properties programmatically, using JavaScript.

Is it possible?

Thank you.

hi, the screensharing whitelist is removed starting with firefox 52, so i don’t think you’ll have to care about those preferences still…
https://www.mozilla.org/en-US/firefox/52.0beta/releasenotes/