A similar question was asked 4 years ago, when Firefox 13 introduced lazy loading: How do I make Firefox 13 Load All My Tabs on Startup or when Resuming Reload
Firefox 13 (Released June 5, 2012) has introduced a new default setting to Load Tabs on Demand. This causes the browser to only restore the currently selected tab when resuming a session on startup, after a crash, or on a requested reload. I really don't like how I now have to click each tab and select restore. How can I turn this off?
My problem is, the solution found there (going to options => "General", or later "Tabs", and then unchecking "Don’t load tabs until selected") doesn't work anymore: since the new version 47, that option seems to have been removed.
Is there a new way to force Firefox to load all tabs when resuming a session?