Ok, thanks. I could zoom previews just a little bit. But my question was for speeddial extensions. I can't zoom speeddial extension using steps you provided.

It doesn't help. Speeddial boxes itself change size when I do ctrl+mouse wheel. But content inside boxes are too big anyway.

I installed Opera 36 on new Win10 machine. And I see this awesome picture:

https://api.monosnap.com/rpc/file/download?id=ygAnIkDi9uck2ehHpLt6XDB1vziQh4

Content of speeddial extension in enormously zoomed in so you hardly could see what's there. I have Medium font size and 125% zoom in settings, so problem shouldn't be there. How it could be fixed?