How do I get Opera browser under Preferred Applications?

I have opera set as my default browser but chrome is set under Preferred Applications and opera isn’t on the dropdown menu only firefox and chrome show

Whiich version of Ubuntu MATE? I think there's a slight bug at the moment with Preferred Applications under 15.10 -- the web browser defaults are not being set correctly.

You could try setting Opera as the default via the terminal, using this command:

sudo update-alternatives --config x-www-browser

oh I have 15.10 I will try with the terminal thanks