Unfortunately it doesn't work at all. I can see all cookies in the cookie manager after a browser restart.

Add-on immediately pops up an obnoxious full page interruption at install -- and then a second one wanting to know the reason why it's being uninstalled, where the feedback form doesn't even work. Cheap attempt at capitalising off someone else's good reputation with a knock-off product.

This does not delete cookies when the browser or a tab is closed as claimed.

Had high hopes but alas does not fit the bill. I Have Gmail multiple accounts open and upon closing Firefox 65.0.2 and then several minutes later I relaunched the browser and reopened Gmail I was still logged in. As far as I can tell this extension does nothing when session mode is enabled.

no cookies are deleted when firefox is closed despite selecting this option in the addon.