Just want to give some feedback. Since i'll keep changing the same flags after every update..
opera://flags/
#search-in-open-tabs -> disable to get resently closed tabs back (i also use this one to open tabs that i have open on other (mobile) devices.
#horizontal-tab-cycler -> disable to quickly switch between recently used tab with a dropdown based menu (that shows the full tabname) in the location of the recently closed tabs.