Horizontal Menu is broken
I use the horizontal menu bar and in the early versions it worked just fine but somewhere along the way it broke, as in 1) no theme coloring in the menus, 2) you cannot close a menu by clicking it again (have to click somewhere else in the browser window) and 3) you also cannot move the mouse cursor to another menu to open it (like in Windows normally). See screenshot: Vivaldi 1.0.380.2 (Developer Build) (32-bit), Windows 7 x64 [img]https://dl.dropboxusercontent.com/u/16860472/vivaldimenu.jpg[/img]
All your described problems are already known or reported as bugs.
I hope in next Beta this will be fixed.
1.0.352.3 is the last version which does not have this problem, if you want to go back for now:
I also noticed that pressing the F10 key does not bring up the menu bar, like it does in Windows.
The horizontal menu is still broken (no click to close, not able to mouse-hover through the menus). Can we expect a fix for that?
F10 can be assigned to toggle the menu bar, but it's still quite badly broken. No doubt it will be fixed sooner rather than later.
Note that if you just disable the menu bar, the menus will open with hover using the Vivaldi Button, and the cursor keys also work there for navigation, which they do not on the horizontal menu bar.
Access keys, Alt F, Alt E, Alt V, Alt T, etc., also work to open the menus, so for now you're much better off not using the horizontal menu bar if you like using the menus. At least in Vivaldi, the Horizontal Menu and the Button Menu are identical, unlike they were in Opera 12.17.