Hey Max! This usually happens after an update or if you're not logged in to your Firefox account. Make sure you're signed in under Settings > Sync and check that autofill is enabled in Privacy & Security > Logins and Passwords. If you've set a master password (now called Primary Password), you'll need to enter it before using saved logins. Updating Firefox or clearing your cache might also help. Let me know if it's still giving you trouble!

Did all that first. Cache cleared logged in.