The following guide makes the best use of Qubes disposible vms and Firefox: https://forum.qubes-os.org/t/guide-automatically-install-extensions-and-configure-new-dispvm-hardened-firefox-profiles-with-arkenfox-user-js-and-policies/11786?preview_theme_id=1
For some personal accounts you may not want a disposable vm, in which case Firefox with arkenfox settings, is a good option, or the Brave browser if you prefer chromium, both of which are in the Debian and Fedora repos. Mullvad browser is another option, but would require more effort to install.