The left and right side panes on the Forum are indeed triggered by swiping from the edges, and I have to admit I was originally surprised by this behaviour when I first discovered it as there's no obvious visual prompt that this feature exists.

Also, a large number of Android apps with page-based navigation (not just browsers*) use side swiping for back and forward navigation - or such is my experience.

*For example, I have an app for bus passes which goes back to the ticket select screen on a left-to-right swipe.

Wouhouh, fixed in the latest snapshot !? 😃
Well done !!!

@nito What I am talking about is not smooth scrolling of the preferences. I have noticed the existence now. When I install Vivaldi, I recommend installing the application to macOS by Vivaldi. I think that it is an add-on attached to it.

Correction: Swipe navigation works intermittently in Vivaldi 1.6 RC!

It was working fine then it suddenly stopped working! If I open a page in a new window and click some links to generate history, it starts working again.

I've reported the issue and hopefully they can get this working reliably again soon.