Another standard feature that's missing in Opera is support for revealing your stored passwords just in case you forget them.
Firefox and Chrome support this and users have come to rely it.
For Opera, you have to resort to using bookmarklets, extensions, userjs or external programs, to get a look at your passwords. You also have to trust that those programs/scripts won't steal your passwords. Or, write one yourself.
Even then, none of those things help for Opera's built-in mail client. For it, you have to attempt to connect without tls (if possible) and use Wireshark to sniff for your password, or use an smtp log while trying to connect via TLS. And, once you get it, it might be base64-encoded, which you'll then have to decode.
And, for programs that can read Opera's wand.dat, they break if you use a Master Password in Opera.
In short, with Opera, if you forget a password and the service the password is for doesn't provide a way for you to retrieve your password, you're going to have fun trying to get it. This is made many Opera users very angry.
With Firefox and Chrome, it's not a problem. You can just simply show your password in the settings.