These are my own configuration overrides for Firefox and Thunderbird, to be loaded on top of the arkenfox user.js and HorlogeSkynet's thunderbird-user.js. Before using these overrides, please make sure to read and understand the wikis available in the upstream project repos.

Download updater.sh, prefsCleaner.sh, and user.js from the arkenfox repo and place them in your Firefox profile folder. Place the Firefox user-overrides.js in this folder as well, then run:

bash updater.sh
bash prefsCleaner.sh

Make sure your Firefox profile is not currently in use while you run these scripts. Also, make sure to rerun the scripts periodically in order to keep your user.js file up-to-date.

Download updater.sh, prefsCleaner.sh, and user.js from HorlogeSkynet's repo, place them in your Thunderbird profile folder, add the Thunderbird user-overrides.js, then run the scripts as above.

Be aware that some of the preferences set by HorlogeSkynet's user.js make it impossible to authenticate into email accounts using OAuth. These preferences are respected by user-overrides.js because they are privacy-enhancing. If you must use OAuth, you need to temporarily flip them by uncommenting the following two lines at the end of the file:

// user_pref("javascript.enabled", true);
// user_pref("permissions.default.image", 3);

Run updater.sh and prefsCleaner.sh to enforce the new preferences, then launch Thunderbird and log into your account using OAuth. Once you are done, clear any cookies, close Thunderbird, comment out the two lines again, and run updater.sh and prefsCleaner.sh to restore privacy-enhancing defaults.