I'm a longtime Opera user and I have to use Firefox right now for an unrelated reason. The feature in Opera that I miss most is the way it used to be so easy to view a gallery. In Opera I would switch to full screen, bring up the gallery, click on 1st photo & there's my full screen picture. Now here's the good part--to view the second picture, I would just press PAGE FORWARD & there would be photo #2, & so on.
Here in Firefox, after I view photo #1, I have to go back up to the full gallery & click #2, and so forth, up & down. It's the same slow procedure in Safari (I've got Mac).
The older version of Opera from about a year ago had a terrific feature--in full screen (F11 on PC) any blank space around the photo, as for a portrait type, was automatically filled in with dark gray. So you would see your model's photo with nothing framing it, like in a movie theater. I wish Opera (and Firefox) would use that feature.