Into Firefox? No you can use it without signing in. However, if you want to sync your account you would have to.

Hi Crispen, Firefox recently had a bug where you had to enter a Primary Password at startup even if you weren't connected to Firefox Sync or trying to sign in to a site using a login saved in Firefox's password manager. That should be fixed in Firefox 136.0.2. See: https://www.mozilla.org/firefox/136.0.2/releasenotes/

If you meant something else, could you explain in more detail?