Pls improve compatibility with 3dmark
3dmark has problem with displaying results when vivaldi is set as default browser, could you please contact with futuremark and work together on changing it? Here is steam thread where i pointed to them this problem as well: http://steamcommunity.com/app/223850/discussions/0/648814842324651309/
This is probably a problem with Vivaldi as it has a bug where if it's not open it won't display a page called from some other application.
You can also try opening the Metro settings panel and set Vivaldi as default there.
FYI, note in the FM_Jamis Steamcommunity post directly above spectatorx's post there that FM_Jamis has observed that Chrome can cause a similar kind of problem because it "doesn't set itself properly for other applications to start". In that case, the problem may be carrying into Vivaldi via the chromium/Blink engine itself (derived from Chrome). The Blink developers may be the best place to communicate the bug information.