On a side note, it is better to use a password manager like LastPass, then using the default browser solution (remember password) or not using anything at all.
There, you could set on which urls, which keys could be used.
Never enter your password/key manually, only through the manager.
If there comes a place, where that the password manager don't give you the option to input your keys, look carefully why. Is it phishing ? Be skeptical.
And don't forget to backup your password manager's data store (or as it is called for LastPass - Vault), preferably in an encrypted, password protected form, at multiple places, at least one of which is cold storage.