Support disabling welcome pages/recommended addons

[jacksonisiah]

These welcome pages are pretty annoying, since they are just ads for the vpn service and such, as well as recommended addons (potentially a privacy risk). I would love to see a toggle for this in ffprofilemaker.

https://support.mozilla.org/en-US/kb/firefox-browser-welcome-pages

Apparently it is related to these settings?

[allo-]

I think this are two features. One are the recommended extensions/features and the other one the welcome-page after the upgrade. The welcome pages probably need an enterprise policy.

{
  "policies": {
    "OverrideFirstRunPage": "",
    "OverridePostUpdatePage": ""
  }
}

This can be added once #220 is fixed, which breaks generating enterprise policies in weird ways.