May I politely suggest, (again), that when you remove an inappropriate topic, there is no need to say this topic is deleted.

It serves no useful purpose.

There is a Chrome extension available that might help ... "Right Click Opens Link New Tab Correct Order".

My apologies if this has been asked before. I have two main browsers; Opera and Firefox.

Firefox has some updated bookmark entries that I do not have in Opera.

If I re-import the bookmarks from Firefox, does Opera start over, so to speak, or will I have duplicate entries?

OP ... I'm running the latest version of Opera on Windows 10. It's as fast as Firefox, if not faster.

Have you done a system scan for possible malware? (try Malwarebytes and SuperAntiSpyware).

Also check to see in the system Task Manager what other (unnecessary) applications may be running.

@gokuluffy ... Agree. This is really getting annoying.

Found the problem. The extension User-Agent Switcher was turned on.

My thanks to all that replied.

YOUR BROWSER SCORES 501 OUT OF 555 POINTS
You are using Opera 48.0 on Windows 10

I am on Version 58.

This is using http://html5test.com. I am on Opera version 58.0.3135.79.

What is wrong here?

For topics that have many posts, there is a "counter" at the bottom of the page. I know this is trivial, but is there any way of disabling this?

@pastel10 ... Try this ..., in Settings, Enable Dark Theme. (which you have done).

Then under wallpapers, select a black wallpaper. That should work.

On my setup, the active tab is a dark gray background with white text.

The inactive tabs are black with white text. I also have minor vision problems and my setup makes it
much easier to read. Hope this helps.

One other thought, disable any tab extensions that might conflict with this.