Wšykne wótegrona (1)
It should be about:config with a colon : as you type about:config in the location (address) bar as you would type in say www.mozilla.org
Here is a kb article explaining the basics of about:config though about:config is meant more for advanced users. https://support.mozilla.org/en-US/kb/about-config-editor-firefox
Another about: url that is useful is about:about
Musyśo se pla swójogo konta pśizjawiś, aby na pśinoski wótegronił. Pšosym stajśo pšašanje, jolic hyšći njamaśo wužywaŕske konto.