Ugh. My comment disappeared when I posted it. Simply this: on the Firefox blog page for split view, it provides clear instructions on how to enter the mode. But it has no information on how to exit split-view mode. I eventually worked it out, but it ...
A simple suggestion for the official Firefox instruction page on split view (https://blog.mozilla.org/en/firefox/split-view/Please include instructions on how to UN-split-view the tabs!!! I eventually worked it out, but it's not immediately apparent...
