Do you use an add-on to prevent that from wiping out all but one window's worth of tabs when you close them? That's what originally made me get a tab grouping addon, after losing a ton of tabs when I broke some out into their own window and then later closed the main tab window before the secondary one. Realized immediately what happened but it was already too late to save that entire generation of precious tabs. Who knows what articles I didn't feel like reading at the time but was totally going to read later I lost forever.