Strong, random passwords generated on your device — pick a length, pick your character types, and get five at a time. Nothing is uploaded or stored.
What makes a password strong? Length, mostly, and real randomness. A 16-character password drawn from letters, digits, and symbols has about 105 bits of entropy — no guessing attack gets through that in any realistic time. A short "clever" password with a word and a number does not come close.
Are these passwords safe to use? They are generated on your device with the browser's cryptographic random number generator — the same source security software uses — and are never sent anywhere. Use a different one for every account, and store them in a password manager rather than reusing them.