as per brokendust: "Yt-Videos have (seems like) randomly lagspikes and a huge loading time. In addition to that, if I want to start/stop a video and click on it, Opera needs ~2 secs to notice what I wanted to do. Even the tab close needs a few sec to get his own function. "

Same here.

And it is the same for embedded videos or directly at YouTube..

When I load the same page in Chrome everything works fine.

My opera version is 36.2 on Marshmallow.

Need further guidance to implement the web app functionality as described here: https://dev.opera.com/blog/web-app-install-banners/

I have used the manifest generator and validated its functionality.

When I browse to my site: https://mysite.com the install banner does not appear. Probably because I do not have a 'service worker'. Need guidance on this.

Second, when I click the plus sign I can add the app to the home screen, but the home screen never shows the icon, nor is it full screen. Still have the address bar and the browser controls at the bottom.

Here is the manifest:
{
"lang": "en",
"background_color": "#ffffff",
"name": "go BillThis - mobile business management",
"short_name": "go BillThis",
"display": "fullscreen",
"icons": [
{
"src": "/Images/bt144.png",
"sizes": "144x144",
"type": "image/png"
}
]
}