This originally started as a comment, but since I wrote so much I decided to turn it into a blog post.
Try otter browser:
It promises to be everything that old opera was, so a bit similar to Vivaldi, except, Otter browser is open source!
since Opera shifted to version 15, I just can not find a browser that I
consider irreplaceable. Because Opera versions 15-25 did not support
Linux I was forced to switch. My choice at that time was Chromium, and
it was generally ok, it loaded web pages pretty fast and youtube just
worked. But it lacks some serious features, plus most of the interface
elements are not made for the widescreen era. And it eats RAM.
as soon as Opera 26 with linux support entered Opera's Alpha channels I
switched back to Opera. At first I liked it, but the more I used it, it
felt like Chromium with gimmicks. And it started to feel unclean to use
a non-open source browser on an open source operating system. I do
however watch Opera's blog and I admit that the latest versions are more
than Chromium with gimmicks, if only it were open source.
gave Firefox a chance, which I still use to this day. I like it because
it is more feature rich than current Opera or Chromium. However some
websites, including Youtube, just don't like Firefox anymore. And
Firefox actually tends to eat my CPU.
Since Vivaldi is not open
source, using Vivaldi is out of the question. I have also tried using
several smaller browsers like Arora(I loved it back in 2011,but now it
is outdated), Epiphany, Midori, Konqueror(I wanted to try KHTML as an
alternative to Webkit)...But most of them had either even less features
than Chromium or they were hated by websites.(Konqueror does seem like
an interesting File browser/Web browser hybrid however).
I have stumbled upon Otter browser by accident when I saw a comment
about it on Opera's blog. And after a few versions of it, Otter browser
looks like a glimmer of light. It is rapidly gaining features every 1-2
weeks. It promises to bring most of old Opera 12.16 features. It is open
source and has a repository on github. The only feature missing for me
to move to it as my main browser is an https everywhere option. Plus it
has a Youtube bug, but due to the youth of the project I am willing to
overlook it. Oh yeah and although I am a Linux user, Otter is one of the very few browsers that still support *BSD!