Here you will describe what the problem is with the most details as possible but being objective and concise.
Press [Ctrl] + [Tab] to cycle through tabs
Thumbnails when tab cycling, tab list pops down
Option to cycle through tabs without thumbnails or tab list as seen on the Windows version: http://help.opera.com/Windows/9.50/en/tabs.html
"Cycle without showing list"
"Show thumbnails in tab cycle"
There is a global option under "User interface" for "Use tab previews" but I prefer the thumbnails when hovering on a tab, not during tab cycle.
OS X 10.11.6