Google Plus's new interface has a problem on Vivaldi
dunno, they both look the same in Vivaldi and Firefox for me (in Firefox I was not logged to G+, I was logged in Vivaldi)
The page looks the same for me in Vivaldi and Chrome, on Ubuntu16.04.
As you can see in those screenshots, the word Advocacy is cut off if the browser window is too narrow. Vivaldi has, by default, a side panel (on the left side of the window) that makes the content area slightly smaller than in Firefox. If your screen width is right on the threshold of the G+ panel's text wrapping into too many lines, Vivaldi's panel will cause that effect.
Beneath Vivaldi's side panel is a button that closes it. Notice however, that your browser's zoom level affects the layout too. G+ will show two columns of posts if you zoom out enough, and that also affects the wrapping of the heading. Zooming is controlled with the slider on the right of the status bar (bottom edge of the window). Alternatively, you can hold Ctrl and press + and - or move the mouse scroll wheel.
It seems to me that the fault is at Google+'s CSS layout. If it's intentional, they're maybe pushing people into using short and catchy group titles… :huh: