It was installed as "for current user" with "show in start menu" option.
I don't think it's OK for developers that installation "for all users" is the only option to make Opera default browser. Tell me if I'm wrong.

Let me wait for this DNA-19636 is resolved before I reinstall Opera for all users (will it be resolved? )

Thank you everyone!

Good day!

Opera 20.0 is not listed in Windows 8.1 x64 browsers, though I installed it on clear system.
There is no possibility to make it a default browser. When I click "Make Opera a default browser" in Opera options menu, a window with "Find a program in Windows 8 Apps shop" and "Internet explorer" to chose from appears. No Opera browser there.

Are there any variants to solve this problem?

Thank you.