There's only one problem – officially it doesn't support newer versions of Gnome(the last supported Gnome version is 3.8). But there's an easy way to make it work in Gnome 3.16+(tested on 3.16 but i'm pretty sure it will work just fine in 3.18 or 3.19 or some newer version in the future). All you have to do is download the extension manually, unzip it and modify the file metadata.json with simply adding your version of Gnome in the list like this:

//… some text here … 
  "shell-version": [
    "3.4",
    "3.6",
    "3.8",
    "3.16"
  ], 
// … something here  …

After that copy the entire "window-options@mathematical.coffee.gmail.com" directory to your gnome extensions folder. In my case (Ubuntu Gnome 15.10) this is:

~/.local/share/gnome-shell/extensions/

and restart the gnome shell:

Alt+F2 -> r

now you just have to turn this on in Gnome Tweak Tool and your're done

Before:

![before] (http://i.imgur.com/UDSjFpS.png)

After:

![after] (http://i.imgur.com/mWO9VwK.png)

P.S. I must say that Opera is the only software of what I use that doesn't have that window control buttons(minimize/maximize) so its really confusing when the devs say its Gnome's fault when it's really not because all other programs have this buttons.

I was thinking of returning to Opera and shockingly after setting up everything I stumbled upon one problem when I want to minimise Opera.. The freakin button is not there.

Running Ubuntu Gnome Wily Werewolf

The thing is, what made me feel a lot sadder is the mere response of an Opera representative, stating that things won't change for what it is.

Those buttons might be useless to you, but could the Opera team at least add them so-called "fake buttons" for the ease of users? Of blame the shell they say! Would you consider removing the window buttons on Windoze? I am sure not, because it is well embedded in the explorer UI isn't it? Well let's say it is possible to remove, will you guys remove it?

The answer will of course No. Because? I am guessing FAMILIARITY. Windoze users has been comfortable with interacting multiple windows by relying on the window buttons available.

But but Gnome has only Close window button by default

Hoh! Fire up gnome-tweak-tools and you can add those little friends back.

But but Gnome original workflow isn't intended for window interaction, but emphasises on workspaces and stuff

Options! OPTIONS! In the gnome-tweak-tool it is possible to add back the window buttons, because not everyone uses workspace! Why they put such options? Familiarity, again. Window buttons are very familiar with any window managers, be it the age old Windoze, Mac and even some major DE you can find on Linux, there are always window buttons. Also they want to make their users happy.

But but it is semantically wrong to use a fake windows button

Remove the fake close button then. Make your users exit via the Opera menu.

Don't like it? Leave it

Hmm I am starting to wonder why developing Opera.. Is it for ghosts?

Seriously it is funny how a simple feature is scrapped off Opera. Like seriously? This has been a very very huge disappointment.

I am keeping a very close eye to the Opera "fake" title bar. I expect to see a maximise and minimise button soon.

If not, well, i can't threat you guys in any means, but i just want to say you guys have a very bad technique on making users interested on using Opera. Also bad way of thinking i must say.

I agree with @Thiasj . I hate posts aired by one of the Opera representative here. It is very unprofessional, and doesn't reflect good attitudes a person must follow when dealing with something that requires general attraction (in this case Opera).

You are pushing users away.

Have a freakin nice day.

any news on getting back the minimize/maximize button on Opera? I used Opera for years (since its gone free) and was excited, that it came back on linux with opera developer! But was disappointed, that opera is yet another chromium clone ... nevertheless it has some better features than chromium ...
Now Im still waiting for that minimize/maximize feature! I dont know why you dont allow gnome3 user to minimize the browser, even with the "middleclick on titlebar" feature in gnome3. I ran opera now since the first opera developer release, but not be able to minimize the browser is a nogo. And if you refuse to implement this feature I will use chromium again.
I hate those "Do this, or I'll leave" posts, but this is a very basic feature, that im using everytime and I wont do without it. I really hope you will change your mind!

Stripping the titlebar as an option? We are not currently planning to. Things might change however.

I don't know how does it work but I meant stripping it (optionally or not, I don't think anyone would prefer to have a useless space up there) for Elementary OS like in GNOME. Thanks for answering

if you right click on the title bar the context menu has an option.

Cool, never noticed that but you are correct. It works!

Thanks for the tip.

Will you implement this behaviour by default in the future? Just to know, I understand that its target is very small

Stripping the titlebar as an option? We are not currently planning to. Things might change however.

You can use a windows matching utility like Devilspie2 to strip the title bar in any window manger
Install Devilspie2 and create a file called ~/.config/devilspie2/opera.lua containing the following:
if (getwindowclass()=="Opera developer") then
undecorate_window();
end

You can then run Devilspie2 as a daemon (-d) and it will strip the titlebar off Opera, when it starts up. If you want it to be maximised as well, try this instead:
if (getwindowclass()=="Opera developer") then
maximize();
undecorate_window();
end

Will you implement this behaviour by default in the future? Just to know, I understand that its target is very small

Install Devilspie2 and create a file called ~/.config/devilspie2/opera.lua containing the following:

if (get_window_class()=="Opera developer") then
   undecorate_window();
end

You can then run Devilspie2 as a daemon (-d) and it will strip the titlebar off Opera, when it starts up. If you want it to be maximised as well, try this instead:

if (get_window_class()=="Opera developer") then
   maximize();
   undecorate_window();
end

If you want more than the close button, leave the native titlebar in place. If not you will have to accept the compromise of only a close button. In any case you can maxmise/restore by dragging and minimise via the task bar, or by assigning a keyboard shortcut.

With titlebar hidden via the method outlined above:

With titlebar shown:

KDE unfortunately doesn't support window manager hints for removing the title bar on maximization

Okay, but Chromium have option "Use system title bar and borders", so we want have the same in Opera.

avl: I can understand why this is. I do have a small issue with it however: When you assign it to the left or right side of the screen (with windows-key + left/right arrow) in GNOME 3. It will detect it as maximized, disabling the title bar. However, if you have multiple tabs open, there is no space to double click somewhere to have it unmaximized. In maximized mode, there is some space next to the "new tab" + icon to to this.

The only way is to use a keyboard short cut again to return to unmaximized mode. This could be resolved by adding the same space next to the "new tab" + icon as in fullscreen maximized mode.

I'm aware of the KDE settings for this, the issue with using them is the fact that I would still be missing the minimize/maximize/close buttons in the top right I'll check if Opera 25 has the ability to add/customize these buttons, but I haven't seen them since Opera 12.x. Thanks again.

KDE unfortunately doesn't support window manager hints for removing the title bar on maximization, but it does offer its own settings that allow you to change when window decorations are enabled and for which applications. This guide shows you how to disable window decorations. It's for Firefox but will work for Opera too (switching out the names, of course):

http://oxygenkde.altervista.org/exceptionsguide.html

Opera's window class name is "Opera developer", you can see this using 'xprop WM_CLASS' (click the Opera window after starting this command to see the information).