@avl Unfortunately I had to migrate back to Chrome. I was too bored with Opera's not playing simple mp3 file (https://goo.gl/Nt1qSg) animated GIF's in Twitter... Instead of improving the browser Opera's team is making regres.
You can find which version comes from where with "apt-cache policy libnss3".
However, both are too old now, because all the working repos of ubuntu (14.04, 16.04 and to 17.10) have 3.28 (2:3.28-whatever), so yes, an update is mandatory for you now.
The developers' Desktop blog is an obvious place to start, and entries there generally link to a changelog.
Most recent Stable release: http://www.opera.com/blogs/desktop/2016/01/opera-stable-34-0-2036-50-update/
Changelog (as linked in the blog) for 34.0.2036.50: http://www.opera.com/blogs/desktop/changelog-34/#b2036.50