WebExtensions are inadequate to handle all http requests

[tumpio]

"Some sensitive requests" are unable to be controlled by WebExtensions by API design. These requests are silently ignored without any exception nor warning.

List of bugs:
https://bugzilla.mozilla.org/show_bug.cgi?id=1380729
https://bugzilla.mozilla.org/show_bug.cgi?id=1380739
https://bugzilla.mozilla.org/show_bug.cgi?id=1334918
https://bugzilla.mozilla.org/show_bug.cgi?id=1330590

Related information:
https://www.ghacks.net/2017/07/13/privacy-blunder-firefox-getaddons-page-google-analytics/

[tumpio]

🙃

[Atavic]

Setting up a local proxy may be one last resort. I also think that the User Agent string customization will have hard times with webextensions.

[tumpio]

There is currently small set of privileged hosts, which are ignored by webRequest API. These may be controllable in future with an explicit permission.

addons.mozilla.org
discovery.addons.mozilla.org
testpilot.firefox.com

In addition to these any Firefox "system principal" request ("any request made by Firefox for itself") is out of the scope of webRequest API.