shishka_b0b

I wasn’t sure what the actual preference name was so the code I gave you wasn’t accurate. This is exactly what you need in the user.js file:

user_pref("sidebar.visibility", "hide-sidebar");

It didn’t seem to work the first time I restarted Firefox even though the value for sidebar.visibility was changed correcty in about:config so I edited it back to always-show and then right back to hide-sidebar and now the sidebar remains hidden on startup

Edit: typo

Put the config settings in a user.js file and save it in the root directory of your Firefox profile. It should look something like this:

user_pref("always-show.config.setting", false);
user_pref("hide-sidebar.config.setting", true);