@mike I like the way #ZenBrowser handles this (at least with this configuration). I have the Fosstodon site pinned (the tab I'm using right now!). When I click a link to a different site, it opens in an in-window pop-up.
For me, these preview-style pop-ups (which you can get at any time by right-clicking a link and hitting "Open Link in Glance") are the killer feature of this browser. #SeeAltText

I'm guessing Vivaldi has a feature like this too?