None of the modern browsers will like a self signed cert, so you will need to save and accept that and get used to the working label on the lock. Generating a new one with a valid date is probably still a good idea but the warnings won't go away.
For the cipher the best available is the 3DES_SHA-1 which should stop that warning on modern browsers.
The certificate is only used when managing the device so only needs to be accepted on devices you use the web interface on.