Hello! Very new to Linux but got a new laptop and installed Ubuntu on it. I've run into some issues logging into sites (specifically iCloud) and somewhere I saw someone say they fixed it by installing Firefox via the .deb package rather than through snap, as it's installed by default. Following the installation instructions here: https://support.mozilla.org/en-US/kb/install-firefox-linux#w_install-firefox-deb-package-for-debian-based-distributions-recommended I've run into a roadblock with adding Mozilla APT repository to sources.list. Copying the instructions for Trixie and newer, I've run into an issue where it's giving 'permission denied'. As I'm new to Linux, I'm not really sure what next step to take, short of just typing "sudo" everywhere to try to get it to accept it. Please assist! I would be grateful.