I blocked Opera's auto-update. When I will update Opera myself, or reinstall Opera -- I expect I will have to redo those registry changes.

Thank you for your response, gwen-dragon. I think your solution is smart, because it still uses the start-up parameters (in a way I did not expect). I implemented your solution in this way:

In the Windows Registry, all occurences of

"C:\Program Files (x86)\Opera\Launcher.exe" -noautoupdate -- "%1"

have a key ending with "shell\open\command", so they are related to opening a file in Opera. I changed all these occurrences into

"C:\Program Files (x86)\Opera\Launcher.exe" -noautoupdate --private --alt-high-dpi-setting=96 -- "%1"

After these Registry changes, when I double click on a file which is being opened by Opera -- then I get private mode, and I get a 96 DPI resolution. So this is really the solution I was looking for. Thank you.

[Opera 27.0.1689.54]
[Windows 8.1 Update 64-bit]
[Control Panel\All Control Panel Items\Display\Change the size of all items = Medium (125%)]

I want to use Opera always in private mode, and I want to use Opera always with a resolution of 96 DPI. The solution I found for this, is to add two parameters to the shortcut to start Opera, like this:

"C:\Program Files (x86)\Opera\launcher.exe" --private --alt-high-dpi-setting=96

This solution is only a partial solution. When Opera is not running, and I double click on a file which is being opened by Opera -- then I do not get private mode, and I do not get a 96 DPI resolution.

Now my question is: How can I set Opera so that it will always run in private mode and in a 96 DPI resolution, without using start-up parameters? (I guess changes in the Windows Registry should be able to do this.)

I do not want to change my general PC configuration, because that will impact other programs than Opera. I do not want to discuss whether it is a good or bad idea to use the private mode or a 96 DPI resolution. I am just looking for a way to always run Opera in private mode and with a 96 DPI resolution, without using start-up parameters. Thank you.

I am using "Opera 27.0.1689.54" on "Windows 8.1 Update 1" with "Windows Classic Visual Style for Windows 8.1/Update 1" from "http://xxinightxx.deviantart.com/art/Windows-Classic-Vs-8-1-Update-1-457573957". In Windows' "Control Panel/Personalization/Color and Appearance", I changed the color of the active window border to very dark blue. (This is the color of the active window border of any Windows program which is active. The text in the top border of an active window is white.)

Now in Opera, when the Opera window is the active window, the Opera tab bar has the same very dark blue color as the active window border. Because of this very dark blue color of the Opera tab bar, the "plus" button on the tab bar (for opening a new tab), is nearly invisible (because of the lack of contrast between the "plus" and its background). I would expect a light "plus" when the background is dark, but it is a black "plus".

How can I make this "plus" better visible (i.e. much lighter, or white), without having to change the color of the active window border?