"Where you were", except for waiting for every page to reload.
Having to wait half a minute on every tab switch to wait for that gigantic mess of enterprise grade websites served from an ancient box on the other side of the solar system to load is not conductive towards concentrated work.
When I lose firefox (usually when power outage) I just cycle through all the tabs with ctrl+tab, by the time I get back to the first one it has reloaded (and the others do so in the background). It's not a big deal.