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Why the FVD Speed Dial New Tab extension was deactivated for Opera?
You may need to ask them
Because it replaces the start page which Opera doesn't want. Opera needs the start page to show promoted speed dials etc.
Also see https://forums.opera.com/post/145425 for why the Chrome version of FVD Speed Dial doesn't work fully in Opera and why there was an Opera version that works around Opera's blocking.