Firefox: View two different browser tabs at the same time(blog.mozilla.org)

https://blog.mozilla.org/firefox/its-a-new-firefox-multi-tasking-extension-side-view/?sample_rate=0.001&snippet_name=8528#utm_source=desktop-snippet&utm_medium=snippet&utm_campaign=SideViewAddonIntro&utm_term=8528&utm_content=PRE