First party isolation stops cookie removal from working

[Lusito]

https://www.ghacks.net/2017/11/22/how-to-enable-first-party-isolation-in-firefox/

Enabling first party isolation stops cookie removal from working correctly.
This is due to an API limitation, which is going to be fixed with this ticket:
https://bugzilla.mozilla.org/show_bug.cgi?id=1381197
Until this ticket is solved, I can't do much.

Everyone who wants to use forget me not needs to disable this setting for now and remove existing cookies manually. Because cookies created when the setting was enabled can not be removed.

[Lusito]

The ticket is resolved and scheduled to arrive with Firefox 59.
A fix still needs to be implemented and made available before the release of Firefox 59.