First, set youtube.com to 125% and close the tab so that there's an exception for youtube in "Menu -> settings -> websites -> zoom".
Then, while Opera is closed, use JSONedit to edit the "Preferences" file in the profile directory. See
opera://aboutfor the location.
Under "Partition -> Per-host zoom levels -> x -> www.youtube.com -> zoom_level", edit the value and save. Try 1.33 to see if that works. It says 127% for me in the UI then. 1.55 gives me 133% in the UI.
Anyway, play around with that.
I downloaded the latest JSONedit . On my Windows 10 Pro system, the path that is listed in Opera's for the profile directory is:
C:\Users\Owner\AppData\Roaming\Opera Software\Opera Stable
Obviously the correct location for the Opera installation files
However, when I browse through that subdirectory, I cannot find a "Preferences.json" file there. The closest file name to that was the "prefs_override.json" file which I checked in the JSONedit application just to see what was in that file and to see if JSONedit worked. The application works well, but the "prefs_override.json" file was obviously not the correct preferrences file indicated in burnou426's post. I've looked seemingly everywhere for this "Preferrences" json file, but I just can't find it.. I have found a preferences file that has no file extension in that location. However, when I open the file with JSONedit, It doesn't render properly. All the text is displayed on one long line and is not parsed as in other files that have a json file extension. Just for a try, I opened the preferences file in Notepad++ (a free programmer enhanced version of MS notepad) and it was just a big blob of concatenated text.
Does anyone have any suggestion's as to where this file is located or is it named something different now???