That made one thing clear: about:unloads lists tabs in the order Firefox would unload if it needed to start closing tabs to save itself. When I clicked the greyed-out tab, Firefox reloaded the page from scratch just as if I had typed the address afresh. From the about:unloads Firefox page, you see the exact order Firefox would unload tabs without ever consulting you. Firefox waits for memory pressure before unloading tabsThe manual option lets you do it before Firefox has toAfam Onyimadu / MUOAfam Onyimadu / MUOAfam Onyimadu / MUOAfam Onyimadu / MUOAfam Onyimadu / MUOClose Afam Onyimadu / MUOAfam Onyimadu / MUOAfam Onyimadu / MUOAfam Onyimadu / MUOAfam Onyimadu / MUOAutomatic tab unloading in the background isn't a routine Firefox housekeeping. about:unloads is useful because it shows which tabs Firefox considers safer to unload.