Delete cookies and site data when Firefox is closed - in regular Firefox (not beta or nightly) this seems to create one device per Element tab.

I think this is related to https://bugzilla.mozilla.org/show_bug.cgi?id=1453699

The summary of that bug is that the "Delete cookies and site data when Firefox is closed" option actually changes how localstorage works (both stopping data being written to disk and, incidentally it seems, stopping one tab from accessing another's localstorage, even if they're on the same domain).

It's not super clear what the current status of the bug is; it looks like a new form of localstorage mgmt is in place now for Beta and Nightly, but that it is not active across mainline Firefox.

Observed in 82.0.2 (64-bit)