You can create a "to read later" folder in your bookmarks, then right click the tab bar in each window and select "Bookmark All Tabs". That's fairly close to wh

You can create a "to read later" folder in your bookmarks, then right click the tab bar in each window and select "Bookmark All Tabs". That's fairly close to what you're describing, and also works with Firefox Sync (though in my experience it's best to keep the number of bookmarks below 5000 for Sync to work well).