Suggested improvements / some bugs
Using latest snapshot 1.0.340.7 (Beta) (32-bit) 1) When scrolling Bookmarks in the left hand panel view, Vivaldi freezes every time, and has to be forced closed through Task Manager, along with each individual instance of open Extensions. Others experiencing this or just me? 2) Tab stacking needs quite precise placement of a dragged tab over another - anything less than a 25% overlap and it will not stack, and anything over 50% and it will simply switch places with the one you want to stack onto. I would suggest letting go of a tab anywhere over 10% - 90% of another tab should stack it. 3) The context menu option to 'Ungroup Tab Stack' should be in [b]bold[/b] and first in the list - not buried half way down. If you are right clicking a tab stack then the chances are you want to unstack it. You could argue its just a "you'll get used to it" thing, but it causes me to pause and look for it each time. 4) Ability to resize the Speed Dial thumbnails without having to resize the whole desktop interface. I have the user Interface Scale set at 85% on my laptop, and that it really as small as I want to take it, but the thumbnails are still the size of elephants feet. Old Opera 12 could resize just the thumbnails and auto fit them to the desktop (depending on your grid size choice) - would be nice to have that in V. 5) When sorting Bookmarks alphabetically, it also sorts the Speed Dial the same way - Speed Dial arrangement should be totally independent of Bookmark sorting. 6) Sorting bookmarks alphabetically mixes both folders and individual bookmarks together in that order - Opera 12 sorted folders first (alphabetically) then under them, individual bookmarks (alphabetically), and so does Windows Explorer. This option would be very welcome indeed. V is a fantastic browser, and getting better all the time - using it full time and uninstalled Opera (version 56,497) already, but do still keep Opera 12.17 for prosperity, and as a reminder of what a perfect browser should be like. What about introducing a 'Donate' function on your 'About' page? I sure there would be plenty of ex-Opera 12 die-hards (and new users) willing to chip in and help financially, especially with how fast this browser is developing and where its going - just a though.
Most of your jhints and complains are already known as reported bugs or UI improvements.
Please wait with patience, Rome was not build in a day and Vivaldi will not be complete in a month