I have this one line as the opera repo

deb https://deb.opera.com/opera/ stable non-free

And yes, it is installed with opera's deb, if you answer yes at the question "do you want opera to update with the rest of the system?".

As for extensions, I use

ublock origin, because the built-in adblock fails to catch a few ads download chrome extension, so as to be able to use chrome's extensions as well autoscroll, because all chromium based browsers on linux lack autoscroll