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I don't think there is a built-in setting that can do that. An add-on can load a page into the sidebar (normally used for Bookmarks, History, etc.). If you want to see how that works, here's an example of an add-on that can do it (I have not tested it myself): https://addons.mozilla.org/firefox/addon/open-link-in-sidebar/ What I do is pull the second tab off the tab bar so it becomes its own window, then use the Windows 10 feature to use the right half of the screen for the new window (hold down the Windows button and tap the right arrow key). Then either Windows asks me what I want on the left side )(showing thumbnails of open windows), or I manually place the other tab on the left side (by clicking that tab, holding down the Windows key, and tapping the left arrow key). Since these are separate windows, they don't scroll together/simultaneously. By the way, Mozilla has a product suggestion site at https://connect.mozilla.org/. If you have time, you could post a feature request there to get into the current feedback stream (or give the thumbs up to an existing Idea if someone else already submitted it). Use the "Ideas" section of the site.