12.x is based on Opera's own rendering engine, Presto and is completely different browser. The first Chromium/Blink version was 15 and was source of great frustration to many long time users.

That didn't work for me. Weirdly, the icon for Adbock Plus appears, but none of the others do.

I just upgraded to Opera 25.0.1583.1 Dev on Ubuntu 14.04 (KDE if that matters in this case.) Most of the extension icons in the toolbar have been replaced by little icons that look like puzzle pieces, but the extensions themselves seem to still work. I tried disabling and re-enabling them, removing and reinstalling the extensions and restarting the browser. The same thing happens when I install one I didn't previously have. Nothing seems to work.

I'll try your suggestion. In principle, I agree with using system toolbars but white Opera toolbars and tabs looked odd with my KDE color scheme. Chromium seems to obey KDE's settings if I set it to use the GTK color theme and set GTK apps to the Oxygen-GTK theme. I think Opera can look good in KDE if did the same thing. Just have a setting to allow Opera to use the GTK+ theme and this should allow Opera to look better in Gnome 3 and Unity in addition to just KDE.

This seems to only happen in KDE, when I went into Cinnamon, Opera didn't show the title bars as normal.

I have a strange issue. Opera Dev 24.0.1558.3 for Linux suddenly started showing system title bars in Ubuntu 14.04. I don't think I did I anything to cause this. I checked the settings and flags to see if there's a way to turn them on or off, but there isn't unless I'm missing something. Does anyone have any suggestions to turn them off?

I got Flash to work by cp'ing the libpepflashplayer.so from /usr/lib/pepperflashplugin-nonfree into /opt/google/chrome/PepperFlash. It's puzzling that the original flashplayer in Chrome's directory didn't work, though.

Congrats on getting out a Linux build! Hopefully in few releases you can get QT support, but it's very understandable that ensuring stability is more important than blending in with every DE right now. Interestingly though, for me Opera manages to look better in KDE than Chromium (obviously that's subjective, though)

I tried editing the flash line in ~./.config/opera-developer/preferences to point to the Pepper-Flash I downloaded from the Ubuntu repositories, since Chrome's flash didn't work. But when I restarted Opera, it overwrote the changes, not unexpected behaviour, but I figured it was worth a shot.

Pepper-flash crashes on any page that requires flash and it doesn't see Flash 11.2