i hecked something up involving tabs
help i don't know what i did or how to stop it
now my tabs look like this
also i am bad at linking stuff
here's a link
Double click or middle click on the border between address bar and the thumbnail pictures, this will hide them again. You can also just drag the address bar up in the same place.
If you don't like this functionality go to vivaldi://settings/tabs/ and untick "show tab thumbnails".