If you install Opera 12.17 (Presto), you can install the Firefox bookmarks into that browser. Then you could try the Bookmark Importer Feature. I believe the way to proceed would be to uninstall Opera 21 completely. Then Install Opera 12.17, per the discussion by leocg at the end of this thread.
https://forums.opera.com/topic/2839/new-install-but-no-bookmarks-import/16
After you have imported Firefox bookmarks into Opera 12.17, install Opera 21 (Blink), and see if the Bookmarks Importer then works.
You can, in Opera 21, have your own homepage, not the Speed Dial if you choose. The ability to do that is in Settings (Alt. P), and then choose how you want to operate on Start up.
And you can, with the Opera extension, "Custom New Page," set your new tabs at something other than the Speed Dial, if you choose.
https://addons.opera.com/en/extensions/details/custom-new-tab-page/?display=en