Thanks for the report.

If you stay logged in after clearing, the most likely reason is that “Cookies” was not selected in the extension options, or “Site data only” was enabled with a data type that Firefox cannot clear per site.

Cache clearing alone will not log you out. To remove login sessions, cookies must be selected. Some sites may also keep sessions through storage, so selecting Local Storage / IndexedDB can be useful too.

I improved the options and error handling in recent versions to make this clearer. Please check the selected data types in the extension options and try again.