not experienced with that browser so had to go read. So far not found out how to handle this mess. Maybe handlers :
Manage how links are handled
Some sites may ask to open special types of links by default. These are called protocol handlers. For example, you can set Opera to open ical: links in Google Calendar’s web app or force mailto: links to open in your email web app. To allow or not allow sites to ask to be the default handlers of specific types of links:
Go to Settings.
Click Advanced in the left sidebar, and click Privacy & security.
Under Privacy and security, click Site settings.
Click Handlers.
At the top, toggle on Allow sites to ask to become default handlers for protocols (recommended).
Click the x next to a handler to remove it.
Or :
Maybe :
Manage desktop notifications
Desktop notifications allow websites and apps to display information about their service’s activities or status. These notifications display on your computer’s desktop even when the browser is minimized. They can alert you to things like new emails, special coupon offers, or if comments are posted to your blog.
You can control how sites deliver notifications. By default, Opera asks you if you’d like a site to notify you. You can choose to allow or deny the site to display notifications, and Opera will remember your choice for future visits to that site. To manage desktop notifications:
Go to Settings.
Click Advanced in the left sidebar, and click Privacy & security.
Under Privacy and security, click Site settings.
Click Notifications.
At the top, turn on or off Ask before sending (recommended).
Click the Add button to set site-specific preferences
So far reading is not specifying a way to stop this add.. but still looking
