the ability to make firefox send custom headers with custom values for all sites via about:config preference

[user17]

i want firefox to have a setting in about:config like netork.http.customheader where you can add or modify values of any headers that firefox sends globally. by default it should be empty or hidden, if the user adds headers that firefox already send with different values then it should override the default values. the preference could look like this. network.http.customheader Cache-Control: no-store, User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:159.0) Gecko/20100101 Firefox/159.0, Expect: 100-continue, Pragma: no-cache