@rtabak
Nothing of the above helped; it was necessary to delete Opera and to re-install it completely. I have the latest version now. Further I have to re-install quick links, extensions. Hopefully this will not happening too often. For now Opera remains the best browser.
I hate it when videos start playing without me wanting them to play.
There must be a way to allow the user to stop this.
Instead of faffing about with customizations like tab colors or backgrounds make something proper useful.