Go to the settings and uncheck:

• prediction service,
• predict network actions,
• send feature using information.

Does this still occur? These are options that will use traffic.

Look at your speed dial entries and check if there are some entries without a thumbnail. If an entry doesn't have a thumbnail, Opera tries to access the site to "complete" the Speed Dial entry. That leads to a some traffic at the start of Opera.

Thanks to you all. Your posts helped me and I could find some further information in the net.

So...

1. That Opera 25 only supports pepper (sgunhouse) is new to me. Former versions worked AFAIK (which doesn't say much...). I'll try the solution from joakimwallden or seek for some other solution. I will not install Chrome.

2. Yeah, as avl said "most popular codec" where Opera is not able to redistribute. Where the provided solution may contain parts of GPL licensed code? Gosh, licenses...

Why not use the native (unity) shortcuts:
ALT middleclick - resize window
ALT leftclick - move window

I never knew the middleclick thing.

The last 2 versions of O25 has a better integration with Unity (with Unity menus). An you don't need this command parameter anymore. Resize handle is working out-of-the-box.

So I have 2 Problems. Unreleated. But perhaps this thread can summarize it, because the information differs.

First: Flash.

The current Linux Mint has adobe-flashplugin 11. Opera 25 doesn't recognize Flash.
Firefox says in about:plugins: /usr/lib/adobe-flashplugin/libflashplayer.so
Opera 25 says in opera://plugins/: Nothing.

How can I enable flash in Opera with my current setup? I heard something about pepper and something else but I haven't looked deeper in it. What does Opera 25 under Linux support and how?

Second: HTML5 Videos.

The current installation and the two installations before couldn't play HTML5 videos (youtube saying: error). I made a:

% cd /usr/lib/x86_64-linux-gnu/opera-developer
% ln -s /usr/lib/chromium-browser/libffmpegsumo.so

Works fine (I have no Chromium installed, only these ffmgeg stuff). Is it true, that Operas version of libffmegsumo.so is a bit broken? Is this above a thing to do? Or should it work without that hack?

Thanks in advance if you can answer some of my questions.

opera-developer --force-native-window-frame=true

Nice. Thanks. Resizing the window is now better. The window looks a bit different. The Opera Menu is now always at the level of the tabs, which is OK for me.

I'm testing Opera 24 Developer on Ubuntu 14 (Trusty) in Unity (standard). Compared to other applications it's a bit tricky to grab the resize handle on the Opera window. There seems to be only 1 px where the mouse cursor changes to the resize icon so that I can resize the window.

The issue is even more noticeable if I want to resize the window top to bottom (making it smaller from top to bottom). There seems to be no area at the title-bar but somewhere at the upper corners beside the tabs. But this area seems to be really small. It works with shortcut keys (activating Window-Menu - going to resise window, using the keyboard to resize).

I doubt that it's an issue with the Window Manager and Unity because other applications have a wider area where the mouse-event (changing the icon to resize) is fired. Some apps like the file manager allow that nearly for the whole area of the title bar.